This page discusses and recommends compatible accessories for iOS devices and our line of Harry's app. Although the page is focussed a lot on Harry's LapTimer, findings apply to most other apps too. LapTimer in particular is pretty "extendable" and allows to evolve a basic installation step by step to a professional data recording kit.
There are lots of discussions on accessories on the forum. In case you have questions, please join a thread or start a new one. Like on the forum, this page is structured in sensor types (with a few exceptions). We rate these sensors with respect to LapTimer use, not in general. The selection of sensors discussed is derived from our experience with the sensor and with the company creating it. Although the selection is pretty extensive, it does not cover every device available. Some sensor not mentioned in individual discussions may be listed in the closing of a sensor type section. And sensors not mentioned at all are likely not recommended at all.
NB: Although this page is updated regularly, things change pretty fast and today's best is probably second best tomorrow.
We do not sell hardware and we are not associated with individual manufacturers. We fully concentrate on supporting you in getting the best possible experience when using our apps. You can help us maintaining this page by using the "Buy From" links below. It doesn't cost extra. The links will select a local store automatically. In case your store does not have the accessory listed, please use the manufacturer's link.
When ordering accessories from other countries (e.g. Europeans ordering directly from an US manufacturer's web site) take care you check shipping costs as well as VAT and other taxes due during import. Regulations vary by country.
Before we go into the details, we want to discuss the smartphone and tablet options available. For the latest Harry's app versions, iOS9.3 is the minimum OS level required. We try hard to always support the current and last major OS version. With 9.3 we are well beyond that currently. We recommend to always use the latest iOS version. There is no need to hop onto it on day one, but after a few weeks it will simply be the version most users use and the basis for our application testing too.
The minimum iOS requirement makes an iPhone4S the last generation supported. The iPhone4S is certainly dated and may run into limits when using too demanding add-ons like high update rate GPS / OBD or when doing video recording in parallel. The iPhone4S is the device with the best video support for LapTimer. This sounds strange as all later models introduced great video features. Oddly, many of the optimizations were not in favor of track day users moving fast around a circuit–instead of focussing a moving object. You will get more "jello effects" for the latest generations compared to the 4S. Except this, the iPhone 5S, iPhone 6, etc are the perfect track companion and the recommended smartphones for LapTimer user. They have the processing power necessary for all the features, have big enough screens, and enough main memory to process videos.
In case you want to use an iPod touch, the 5th generation (and later) is supported. Please keep in mind you will need an external GPS on top, iPod touches do not have a GPS chip built in. The iPod touch 5th gen comes with 512 MB main memory - which is the minimum required for video overlaying and processing.
iPads make great track companions too. Like iPod touches, the Wi-Fi only iPad versions do not come with a built in GPS chip and need to be extended by an external accessory (see below). All iPads except the first generation are supported currently. An iPad or iPad mini with 1 GB of main memory is recommended. Most of Harry's apps are optimized for iPads and feature additional layouts to fully use the large screen.
Storage size in another spec you need to take care about. While a 16 GB device is fine to use LapTimer in standard mode (no videos), it is getting a cumbersome operation once you start working with videos. Keep in mind, a minute of Full HD video requires approximately 190 MB of storage. This means a typical session of 20 minutes will require around 4 GB for the raw video alone. Exporting an overlaid video will double this requirement. The recommendation when recording and processing videos is to go for a 64 GB or better device from the beginning.
A stable mount is the only accessory besides a power supply one needs to start using LapTimer. A mount is used to install the smartphone in a place it has both perfect operating conditions (like good GPS reception and a low amount of vibrations) and can be monitored by the driver. Please never use LapTimer without a mount - like placing the smartphone in your cloth or in your car's center console. You need to be serious about this when attending track days.
There are plenty of mounts available today, in all colors, shapes, sizes, and prices. Only a very small number of mounts is well suited for track or other heavy duty use. We have tested dozens and were almost always disappointed. The selection shown here covers some mounts produced by RAM Mounts(R). RAM Mount has an incredible big portfolio for all kinds of vehicle types, mounting positions, and smartphone form factors. They are not the only ones to provide usable solutions, neither all of their mounts are suitable for track use. So please read this section as our recommendation on devices we have experience with. Use a slightly different one (e.g. one made from composite instead of aluminium, or one with a smaller suction cup), and you will get completely different results.
RAM Mount Suction Cup plus Adapter for Cars
The full description is "RAM Twist Lock Suction Cup with Double Socket Arm and Diamond Base Adapter; Overall Length: 6.75 in". The product number is
RAM-B-166U. This is kind of the mother of mounts used with LapTimer. It is super
stable and allows to position the smartphone in a way it has a free field of view (for video recording). Please do not opt for the cheaper
composite version! When installing, make sure you place the suction cup in the top of the windscreen and let the arm point down. To attach your
iPhone to this mount, please add a model specific cradle: iPhone6 Plus RAM-HOL-AP19U,
iPhone6 RAM-HOL-AP18U, iPhone5 (all types) RAM-HOL-AP11U,
iPhone4 (all types): RAM-HOL-AP9U. Generic cradles (X-Grip) will degrade stability.
As introduced above, RAM Mount provides several other options. The above two examples are the ones used most frequently. In case you do not want to, or cannot use a suction cup, you may opt for a RAM Flex Adhesive Base with 1" Ball (RAP-B-378U) or a RAM Rail Base (e.g. RAM-B-231U).
GPS and GNSS
All iPhones supported by LapTimer come with an internal GPS sensor and can be used for lap timing out of the box. However, if you are interested in higher accuracy and use LapTimer a lot, I recommend the use of an external GPS accessory. For iPod touch devices and iPads (non-3G) it is a different story. They do not have an internal GPS sensor (network triangulation only) and thus cannot be used without additional sensor support.
For iOS devices any Bluetooth GPS connected needs to be Mfi (Made for iPhone) certified. This is the reason most GPSes you can buy will not work with your i-device. In addition, there are two approaches for LapTimer to receive data from GPS devices: direct access or using iOS's Location Service. The later works with all Mfi GPSes but limits data to what is passed through by iOS and limits update rates in addition. This is the reason we recommend GPSes connected directly and list these only.
Dual XGPS 160 (Sky Pro)
The Dual XGPS 160 is LapTimer's work horse currently and will provide very good data recordings for most users. It delivers 10 positions per second (10 Hz) and utilizes both the U.S. GPS and the Russian GLONASS system. Using both systems has its advantage in having nearly double the number of satellites available–yielding better accuracy and better lock stability. The XGPS 160's ability to connect to several devices at once does not look like a key feature initially, but saves you from conflicts when accessing it with more than one smartphone. LapTimer is fully integrated with all of this device's features.
Bad Elf GPS Plug-in
The Bad Elf GPS for Lightning Connector delivers 10 positions per second (10 Hz) and utilizes both the U.S. GPS and the Russian GLONASS system. Using both systems has its advantage in having nearly double the number of satellites available–yielding better accuracy and better lock stability. The Lightning connector is making this a unique device in the iOS world. It provides a reliable connection without problems from wireless connections. When using the power pass through option, take care to fix the cable (vibrations). LapTimer is fully integrated with all of this device's features. In addition, LapTime is compatible with Bad Elf GPS Pro, Bad Elf GPS Pro+, and the Bad Elf GNSS Surveyor devices.
Racelogic VBOX Sport (1st gen)
For iOS, Racelogic's VBOX Sport is the fastest GPS available currently. It delivers all data LapTimer uses at a rate of 20 Hz. This update rate is actually beyond what most users will need but an impressive output. The device uses GPS only but is able to deliver corrected data even at 20 Hz. Racelogic is a well known expert in track data recording equipment, something the VBOX Sport clearly benefits from. When opting for this solution, we strongly recommend to attach the external antenna offered. We found the antenna built into the device to be not en par with the rest of the package. NB: this GPS is supported at 20 Hz by LapTimer GrandPrix only.
Racelogic VBOX Sport (2nd gen)
For the second generation VBOX Sport sold since July 2019, Racelogic has changed the chipset. While the first generation device supported GPS only, the second generation uses both GPS and GLONASS. The benefit is better lock stability and better accuracy in difficult conditions. On the other hand, the new chipset samples at 10 Hz only. Although one can argue this is not a relevant parameter due to interpolations applied, it certainly removes a big differentiator the VBOX Sport had for the first generation. In case you can get your hand on a first generation device with an external antenna, you probably get the best of both worlds for a smaller price.
The APEX Pro is not just a plain GPS devices. It is coming with its own set of functionality to improve your driving style utilizing a band of LEDs. Besides the rigid and well manufactured case, this is the reason it is coming at a higher price point compared to consumer level GPSes. For those going the path from APEX Pro to Harry's LapTimer, we have added a full integration to utilize the 10 Hz GNSS stream provided. In addition, LapTimer adds automatic calibration allowing you to use the device without the APEX Pro app. Like for all helper apps provided with accessories, the APEX Pro app must not run in background when using LapTimer!
Dual XGPS 150A
The Dual XGPS 150A is the 160's predecessor and has been the former recommendation for LapTimer. Other than the 160, it comes with a 4 or 5 Hz GPS only chip (i.e. no GLONASS support) and connects to one smartphone at a time. In terms of integration and capabilities, we consider it the same value for money like the 160, making it the recommended solution for price sensitive users. NB: the XGPS 150A often comes with a 1 Hz firmware preinstalled. To enabled 4 or 5 Hz operation, please sign up for the fast firmware here.
Emprum Ultimate GPS
Emprum's Ultimate GPS plays in the same league as the Dual XGPS 150 and shares its GPS capabilities. It is a 5 Hz devices plugged into the old 30 pin port used by Apple up to the iPhone 4S. In case you want to use it with an i-device featuring the new Lightning port, adapters are available. Due to the plug in approach, the handling is somewhat different: the device does not need separate charging as it is powered by the iPhone. It comes with a micro USB port which allows charging the iPhone with the Ultlimate attached. The downside of this construction is it is getting a bit too fragile for car and motorbike operation.
As introduced above, Mfi devices not mentioned in the list are not directly integrated into LapTimer and are not recommended. We add direct integration for all devices we get support by the manufacturer. Please contact the manufacturer in case you want to use their devices for any reason. The following Mfi devices are not recommended due to missing support: Garmin Glo, GNS (all devices).
With introduction of our developer program, device manufacturers and other 3rd parties can add support for arbitraty sensors to LapTimer and friends. The following devices are predefined in our apps and can be used "out of the box". As we do not have access to this devices, any support needs to be provided by the manufacturer or by the person who provided the intergration using our developer program. ReDrive BLE (20 Hz GPS) integration has been contributed by Mateusz Szczurek. Racebox (10 Hz GPS) integration has been contributed by Dmitry Borodaenko. RaceHF (high update rate combined GPS / engine sensor) integration has been provided by 李政 (Le Zheng).
Last not least there are two legacy GPSes LapTimer supports: PosiMotion's G-Fi and Tom Tom's first generation car kit. Both devices are 1 Hz only and are not available any more. Nevertheless, we keep support included already. In addition, any GPS making an NMEA stream available via Wi-Fi can be connected. Samples are several marine devices and the π-GNSS.
A final remark on jailbroken iPhones: in case your device is jailbroken, there are two solutions available to connect any NMEA GPS (i.e. not Mfi) to iOS: roqyBT and BTstack GPS. GPS mouses connected using this solutions will not benefit from LapTimer's direct integration like Satellite View, but work otherwise. We do not support this configurations and discourage the use of jailbroken devices in general.
OBD II and Combos
The following section shows a number of genuine OBD II dongles supported by LapTimer. I'm aware there are a lot cheaper ELM327 copies around but I discourage their use. Although LapTimer will connect to most – if not all – ELM327 wifi dongles, my recommendation is to spend the money for a genuine ELM 327 dongle like those listed. It really makes you feel better because you know what you connect to your car's bus. Furthermore we consider all these knock offs to be product piracy hurting those who invest in innovation.
Besides the discussion below, we regularly run benchmarks on OBD II update rates achieved with LapTimer. Up to date results are available in this thread.
PLX Kiwi 3 and 4
This adapters join PLX's iOS and Android product lines (WiFi and BT) using Bluetooth Low Energy (BT LE). BT LE is available for iPhone 4s and later and works
around Mfi (Made for iPhone) limitations and complex connection making. Update rates measured are en par with GoPoint's BT1 for non CAN vehicles, and faster
then the BT1 for CAN cars. This is quite interesting given BT LE provides by far less bandwidth compared to standard Bluetooth. The Kiwi3 has replaced the
GoPoint BT1 as the standard accessory for Harry's LapTimer users. It is reliable, offers high compatibility, and is very easy to use. NB: the Kiwi 4 needs to
be set to Smartphone Mode to work with our apps. Update rates for the 3 and 4 are the same.
There are three approaches to design accessories compatible with both iOS and Android: use Bluetooth Low Energy, use Wi-Fi, or use Bluetooth SPP and certify
it using the Made for iPhone (Mfi) program. While OBDLink started with a Wi-Fi approach (see the MX Wi-Fi below), it switched to the Bluetooth SPP option
with its latest OBDLink MX+ adapter. The MX+ shows about the same update rates as the
Kiwi3 or the BT1 for iOS, but yields considerable higher speeds for Android. So it is a good option for users who want to stay independent. In general,
we like OBDLink's products a lot. They do their own chip development and have in-depth knowledge. In addition, their own OBDLink app is the best one we
know for tweaking OBD. NB: this Mfi device is not white listed for Dyno currently.
This is another ELM327 compatible adapter using Bluetooth Low Energy. It shows a solid performance and good build quality. Like for the Kiwi3, rates are
limited by Bluetooth Low Energy bandwidth. Both are about the same speed with the Kiwi showing slightly better results. The TONWON's unique advantage is
its low price-there is not a lot you can do wrong.
VEEPEAK OBDCheck BLE
And yet another ELM327 compatible adapter using Bluetooth Low Energy. We have added a predefined sensor integration to our apps for this one too. It is
working out of the box for app versions 23 and later. In case the sensor connects, but doesn't sent data, please try setting your car's bus protocol
in Expert Settings / OBD Tweaks / Default Protocol. Other ELM 327 compatible BT LE adapters can be added using Custom BTLE OBD Adapters in LapTimer's
GoPoint's BT1 and BT1A adapters are Apple certified (Made for iPhone) and connect to
the i-device using Bluetooth. Although LapTimer has some optimizations built in, it is not the fastest OBD II connector you can buy today. But what it makes
it outstanding and the adapter selected by many users is the convenience of use and general communication stability. It is as easy as pairing it with your
iPhone, plugging it into the OBD port, and forget it. It will simply work. BT1 is for Apple users, BT1A is for Apple users who want to keep it in case they
change to Android at some time. Please make sure you update the firmware to 177.0.6 or later.Availability of device
and GoPoint support seems to vary a lot the last years. NB: this Mfi device is not white listed for Dyno currently.
RaceCapture (Track, Pro MK1/2/3, Apex)
The devices for the specialists. RaceCapture devices come with a higher price tag than other adapters on this page, but offer huge value for money and pro level sensors. All of Autosport Labs' devices are integrated into LapTimer GrandPrix now. LapTimer pulls a defined set of GPS and engine data as described on the forum. Please make sure you set your device configuration accordingly. All but the Track device connect either to a standard OBD II port, to CAN directly, or allow the connection of individual analog and digital sensors. Data rates are up to 50 Hz. Keep in mind these beasts require some fun and skills in tech tweaking from you! For iOS, WiFi options are required.
OBDLink MX Wi-Fi
Kind of the opposite to Bluetooth Low Energy adapters, the OBDLink MX Wi-Fi adapter
is incredible fast, but more complicated to use. The adapter creates a Wi-Fi network the i-device needs to connect to. As long as this connection is not
disturbed by other Wi-Fis or the connection is lost because the smartphone picks another Wi-Fi, you will get incredible update rates. As an example, for
a Porsche 997/2, the MX pulls 17 full PID sets a second, were the BT1 is at 8 only. One more word of caution: a smartphone can connect to one Wi-Fi at
a time only. So in case you connect to an action cam (they are using Wi-Fi mostly), you need to choose a Bluetooth OBD adapter.
Automatic 2nd Generation Adapter
Automatic's 2nd generation OBD connects to the smartphone using Bluetooth-allowing other Bluetooth and Wi-Fi accessories to connect at the same time. Automatic considers this adapter not a technical solution, but the entry to an automotive ecosystem of functions and services. Its use is authorized when connecting it to LapTimer the first time. Please do not get confused with the specs: it has a GPS and an accelerometer built in too. These features are not used by LapTimer but Automatic's own app only. The joint use of LapTimer and Automatic's app has a negative impact on the update rate it can provide. Although the raw rate will be as high as 10 Hz, data is actually coming in at 5 Hz or less. Especially for non CAN car busses, you will run into trouble. In case you have an Automatic and a CAN car, this is a nice solution nevertheless. NB: this Mfi device is not white listed for Dyno currently.
Today's smartphones come with great internal cams contributing awesome material to add overlays using LapTimer. Nevertheless, there are some limitations making external solutions interesting. For spectacular driving videos, a wide field of view is what you want. Action cams listed below all come with wide angle objectives. For iPhones in particular, there is another reason you may opt for an external solution: although the cams became better and better for each generation, video stabilization and other "smart" controls are not optimized for track use. They are made to focus a moving object, not for a fast moving landscape. We try to disable as much as possible, but late iOS and Android versions treat all of this as 'hints' and will override LapTimer settings if they believe it is appropriate...
Opposed to LapTimer, Harry's Camper uses external cams to make a rear view available. There are cheaper solutions available than action cams, but why not use them if you have one anyway?
GOPRO HERO5, 6, 7 BLACK AND SILVER
The latest and greatest HERO generation is an incredible cam to record videos on track. While this HERO models comes with a number of new features compared to the HERO 4 generation, it does not really have an advantage when using it LapTimer focussed. As an example, the HERO's GPS cannot be used for data recording. The new HEROs support browsing through videos on the cam's SD card. It is even possible to download videos from within LapTimer. This means there is no manual operation necessary when overlaying videos recorded externally. Like for the HERO 4 gen, connection making can be a bit cumbersome as it utilizes both Wi-Fi and Bluetooth. Please plan exchange batteries or an external power supply.
GoPro HERO4 (Silver, Black, Session, Plus, LCD)
Although the HERO4 has been replaced by later HEROs, it is perfect for using it with LapTimer. We like the Silver Edition in particular, because it supports all cam modes LapTimer can process and has a nice back side touch screen allowing field of view adjustments easily. It allows browsing through videos on the cam's SD card and it is possible to download videos from within LapTimer. This means there is no manual operation necessary when overlaying videos recorded externally! Connection making can be a bit cumbersome as the HERO4 introduces some dependencies between Wi-Fi and Bluetooth. Common for all HEROs is the lousy battery time. Please plan exchange batteries or an external power supply.
GoPro HERO3/3+ (All)
GoPro started a trend when introducing their line of HERO action cams. Although not the latest model any more, the 3 and 3 plus series is still an up to date model and used by many friends of dynamic sport clips. We are official GoPro development partners and are able to provide a much better integration between LapTimer and HEROs compared to initial experiments. To automatically record videos in parallel with data recording, LapTimer GrandPrix is required. GoPro's HERO3/3+ is connected to the smartphone using Wi-Fi, keep that in mind in case you want to add other accessories. Not all of LapTimer's latest features are supported for the HERO3/3+, automatic transfer of footage from cam to smartphone in particular. For more information, please check the Video Documentation.
Sony has made Wi-Fi remote controlling available for many of its latest cams. The full list is available on Sony's website. Like for GoPro HERO cams, connections are made using Wi-Fi. This in turn blocks any other accessory using this channel (e.g. OBD Wi-Fi adapters). The range of video quality is as big as the number of supported devices is. Choosing the Sony HDR-AS200 as a typical action cam, video quality is mostly considered a bit below the HERO counterpart, but the price is lower too. Features supported by LapTimer (et al) vary by model. Oddly, Sony has decided to cripple the cam's interface in several areas. This is the reason LapTimer does not support access to videos on the cam currently. Instead, you need to copy footage manually just like for the HERO3. We plan to find a workaround for this in the future.
Garmin VIRB Cams
Support for Garmin's VIRB X, VIRB XE, and VIRB Ultra 30 has been added recently. Like for most action cams, connections are made using Wi-Fi. This in turn blocks any other accessory using this channel (e.g. OBD Wi-Fi adapters). Like for Sony's cams, LapTimer does not support direct access to videos on the cam currently, footage needs to be transferred manually. No big deal, direct transfers are a lot faster anyway.
I'm contacted frequently with the question if action cam XY is compatible with LapTimer too. The answer is "any external action cam recording H.264 encoded HD and FullHD videos can be used to provide video which can be overlaid by LapTimer". This statement however focusses on compatibility of video material, not remote controlling or integrating the cam with LapTimer. A tight remote controlling integration including easy synchronization of data recordings and video is provided for the above cams only. For all others, the cam needs to be operated manually, synchronization needs to be added by the user, and transfer of footage from cam to smartphone is a manual process too. All of this is described in Video Documentation.
Please understand I will not add further cam support as long as the cam manufacturer does not offer a public developer program, or offers individual support for integration. I contacted many in the past but found most of them not interested in 3rd party support.
When talking about tire management, we see two major dimensions: Tire Temperature Monitoring Systems (TTMS) and Tire Pressure Monitoring Systems (TPMS). The later is mandatory for new passenger cars today, so we see a quick adoption. This type of sensors is focussing on avoiding accidents, fuel economics, and on detecting a hazardous state of the tires. Oddly, access to this data is not standardized, so adding some after market sensors will be required to allow access by our apps. Expect for blow outs, pressure management will work fine at low update rates.
Temperature monitoring is by far more interesting when on track. An optimized tread temperature is a vital measure for optimized grip. When too low, grip will be low, and when too high, tires will wear very fast. Especially with high update rate sensors (5 Hz and more), it is possible to detect critical driving conditions on corner level.
RejsaRubberTrac is a 16 temperature per tire solution (TTMS) developed by Magnus Thome. You can find in depth information on this Maker project on
github. For those not afraid of Maker projects, this is the tire management solution to go for.
Using either 2 or 4 sensors, you will be able to sample tire tread temperatures at around 7 Hz. This update rate allows in detail analysis of tire behavior
and is a great tool for chassis / gear adjustment works. Hardware costs are around 100 US$ per tire, which is only a fraction of cost you pay for solutions like this
elsewhere. Besides 16 temperatures, the sensor is coming with a distance sensor allowing to analyse suspension and tire movement.
The Texense INF-BS is a 10 Hz high update rate TTMS sensor.
Other than RejsaRubberTrac, it is coming ready to use. The device is installed in the fenders of your car with
the termal sensor pointing to the tire surface. With one temperature value measured per tire, installation and calibration is comparably simple. The sensor is coming
with a case that can be put on the sensor body. The case will turn off the device and make sure the sensor lense is not getting dirty. This is the ideal accessory in
case you are focussing on driving style analysis. NB: other than most BT Low Energy devices, these sensors need to be paired with your smartphone before using it
with our apps.
Nonda's ZUS solution is a combined TPMS and TTMS sensor. Other that the track focussed devices discussed above,
it is focussed on safety aspects of driving in general.
The four sensors replacing the ventil caps will send updates on temperature and pressure measurements to the central unit at very low rates and at most when changes occur.
Pressure monitoring can be considered a convenience function when on track. Temperature precision is not clear, but the sensor will allow you to see temperature development
during a session of several laps. Compared to the many no-name devices based on VC601 chip, Nonda's accessory is nicely manufactured. The central unit will issue warnings on
unexpected tire conditions independent from an app connected.
Health and Fitness
The list below is an arbitrary selection from sensors we got our hands on. Different to other sensor types described on this page, we have no market overview yet. In case you find a sensor showing good results and feeding data into Health Kit, please let us know.
The Apple Watch is not a dedicated health and vitality sensor. Actually it collects heart
rates only (but does a lot more). For Watch OS 1, collecting heart rates at reasonable speeds can not be triggered by a 3rd party app. Instead, you need to start
Apple's Workout app before entering the track. Once this is done, the watch samples 10 values per minute. This is less than other sensors, but probably good enough
to do some analysis. Without starting a work out, the watch's sampling rate cannot be predicted - maybe 1 value every 10 minutes. We expect to be able to provide
much better sensor control once Watch OS 2 gets available.
Apps featuring weather options come with support for an arbitrary number of Texas Instruments' SensorTags. This little Bluetooth Low Energy device is coming with a variety of sensors, namely temperature, humidity, pressure, accelerometer, gyroscope and magnetometer. Due to the use of BT LE, the battery included has enough energy for month and years of operation. By adding more than one tag, you can measure different areas - inside and outside - in parallel.
In addition to environmental measurements, Harry's Camper uses the accelerometer included to allow remote leveling. The sensor is sitting inside the caravan and sends information on corrections necessary to the app the user carries around.
All environmental sensors shown here use Bluetooth Low Energy. There is no pairing required like for regular Bluetooth accessories. NB: They will not show up in iOS's list of paired Bluetooth devices. Nevertheless, to use the sensors, Bluetooth needs to be turned on. The first iPhone generation featuring Bluetooth Low Energy is the iPhone4S.
Texas Instruments SensorTag
The TI SensorTag (CC2541) is an inexpensive device hosting several environmental sensors.
Connection to the i-device is made using Bluetooth Low Energy (iPhone 4S and later). Harry's apps will recognize the device automatically, no configuration is required.
As no wired energy supply is needed, the device can be installed easily in any location. Take care to install the latest firmware version for the SensorTag. Firmware
updates are applied by installing the free SensorTag app from AppStore. At the time of writing, the latest version is 1.5 (and the SensorTag is coming
with 1.4 pre-installed). Update rates and accuracies are lower than those of the sensors built into your iPhone, so the sensor is not supported for on track
acceleration measurements. To turn the device on and off, shortly press the power button. In case you run into connection problems, you can reset the sensor by
pressing the power button for 5 seconds. NB: the tag will automatically power down when not used a longer time.