Distance / Sensitivity

Bluetooth - first some history

Bluetooth is not an absolute science when it comes to distance calculation/measurement. The standard was developed in the 1990s to enable connectionless and connected transmissions from point to point and from point to point.  Ad-hoc to make this possible.

The accuracy of distance measurement with Bluetooth is limited and depends on various factors. Here are some reasons for this:

• Bluetooth standard: The Bluetooth standard (< version 5.0) was primarily optimized for data transmission and was not specifically designed for high-precision distance measurements.
• Signal strength (RSSI): The most common method for distance estimation is based on measuring the received signal strength (RSSI). This decreases with increasing distance, but this decrease is not linear and is influenced by many factors, such as
  • Environment: Walls, furniture and other obstacles attenuate the signal and distort the measurement.
  • Antenna characteristics: The alignment of the antennas plays a major role.
  • Interference: Other radio signals can interfere with the Bluetooth signal.
• Multipath effects: The signal can be reflected by various objects, resulting in multipath propagation and inaccurate measurement.
• Inaccurate models: The conversion of the RSSI value into a distance is based on mathematical models that make simplified assumptions about the propagation of radio waves. However, these models can be inaccurate in real environments.

After various development stages (...3.0 / 4.0 / 4.1 / 4.2 / 5.0 / 5.1 / 5.2...), Bluetooth has now become an integral part of Nearfield Communication (NFC). With version 4.0, a very energy-saving version was also introduced by the Bluetooth Special Interest Group (SIG) BT 4.0 LE (Low Energy) has been adopted.

With BT 5.1, the so-called Direction Finding or Radio Direction Finding (RDF) and solved the problems with distance measurements and proximity detection. The standard enables mobile devices to recognize the direction and proximity of objects very precisely.

The introduction of a phase ranging technology called Bluetooth® Channel Sounding to support secure ranging applications as part of the further development of Bluetooth® LE is also intended to further improve distance measurement. (Source)

Smartlock and Bluetooth

I do not know which BT standard Stromer works with. However, indications point to a version lower than 5.0 as only one connection is possible. The distance measurement problems mentioned above therefore also affect the Omni. After a revision of the function (SUI FW 4.2.1.8 from 21.10.2019), Smartlock works better, but still has a tendency to be erratic.

The 'DISTANCE' setting (10 levels) can be used to determine the distance at which the Stromer is unlocked. This means:

• 0 - Smartlock only responds when the smartphone is virtually resting on the Omni
• 10 - Smartlock responds at 10m or even more. It is the most sensitive transmission/reception range setting.

In principle, this is how Smartlock works in practice:
If you approach the Stromer from outside the BT area, the Stromer usually unlocks without any problems. If you are in the BT area but do not drive off immediately and the Stromer locks again, you have to move out of the area so that a new unlocking process works again.

Practical experience

> See read the detailed practical article by 'Xeneticles' in PROBLEMS - SMARTLOCK - 'Practical experience'

Update: SUI FW Version 4.5.0.3 (05-03-2025)

Stromer writes in the release notes for the FW upgrade:

The legacy SmartLock (locking and unlocking via classic Bluetooth) will be replaced by the new BLE version in conjunction with the Stromer OMNI APP. Users who are currently still using the older version (in Omni > MENU > BLUETOOTH > SMART LOCK) will receive a corresponding message**. The Stromer OMNI app must be reconnected in the Omni via MENU > BLUETOOTH > OMNI APP. SmartLock via Bluetooth BLE only works if the Stromer OMNI app is at least running in the background. The function is not active when the app is completely closed.

**Note in the Omni

Sensitivity adjustment is now only possible in three stages and via the Omni app.