BLE reliability and range for safety-critical alert transmission (>60 m, sub-second latency)

[Kai St]

Hi there!

We are currently evaluating a low-power BLE system for a safety-critical wearable application that must transmit immediate alerts to a nearby receiver or mobile device.

Our requirements are roughly:

– Range: stable communication at >70 m (open field) between two BLE devices, but often used also in an urban surrounding where the range should be at least around 30,
– Latency: alarm message delivery within <1 s
– Reliability: minimal packet loss or false-negatives, even in dynamic environments (body movement, multipath, partial obstruction, etc.)

We would appreciate your insight or thoughts on the following points:

1. What is the realistic maximum reliable range for BLE (1M vs Coded PHY) in such scenarios?

2. How stable is BLE signal transmission under moderate body shadowing or environmental attenuation (e.g. when one device is worn on the wrist)?

3. Would you consider BLE sufficiently robust for a critical alert link, or would you recommend an alternative approach (e.g. proprietary 2.4 GHz, Sub-GHz, or hybrid)?

4. Is there a specific Nordic chip which would you recommend for a safety-critical set up?

Many thanks in advance for your advice!

All the best,
Kai
Kai

[Simonr]

Hi Kai

Before I get to answering the questions. Note that BLE will never be 100% reliable or safe if this is to be used in a life or death matter we can't recommend that. Potentially look into a proprietary communication protocol for reliable comms like ESB or ANT+ for example.

1. Based on the use case you have given, as long as there aren't multiple other 2.4GHz devices in the same area. 1Mbps should be fine up to 70m in an open field without interference and Coded PHY should be more reliable, but might not be able to deliver an alarm within 1s as Coded PHY communication takes longer.

2. With good antenna design it should be pretty stable, but again, due to Bluetooth as a whole not being 100% reliable it can't be expected.

3. No, not for a critical alert link.

4. The nRF54L series should be capable of this, but not with Bluetooth LE I'd say.

Best regards,

Simon

[Kai St]

Hey Simon,

thanks so much for your detailed and honest feedback — that’s extremely helpful!

To clarify our approach: we are indeed aware of BLE’s limitations for safety-critical communication and are therefore considering a dedicated RF link between two devices.  The BLE option was a recommadation of a development partner but we are (as you also wrote) sceptic if the connection would be reliable enough.

Our current plan is to use a sub-GHz link (around 868 MHz, EU) with a proprietary ACK-based protocol (including retries, frequency hopping, and AES encryption) for the primary alarm transmission, while BLE is used only for non-critical functions (configuration, logging, OTA updates).

From your experience —

• would you consider such a proprietary sub-GHz approach significantly more reliable and deterministic than BLE for safety use cases?

• and which Nordic SoC or transceiver would you recommend as the most suitable hardware basis for this type of setup (range ≈ 70 m, low latency < 1 s, low power)?

We’re trying to find the right balance between reliability, power consumption, and integration effort — any guidance on the best-fitting Nordic solution would be highly appreciated.

Many thanks again for your time and expertise.

Best regards,

Kai