I have now tried frequencies spaced 50 kHz apart from 868.0 MHz to 870.0 MHz (i.e., 868.0, 868.05, 868.1, 868.15, …), but I get nothing. It has taken me a couple of days. I presume that the smoke detectors transmit on a regular basis, and presume that waiting 15-30 minutes at each frequency should give me something if they are, in fact, transmitting within such an interval.
Do you guys also use the hub, or do you just have the smoke detectors? I have the hub and have paired the detectors with the hub, and I wonder if it could be that the pairing in some way modifies the communication.
I have also, by the way, set the rtl frequency to 433.92 MHz to check if it finds some temperature sensors I have, and it does, so it does work - but I have not had success with the smoke detectors.
Any suggestions are welcome 