I agree with Tim. You shouldn’t be getting ??? in the first few days (as you stated, day 3). Where are you placing them and do you go over a week with any sensors? How long have you had your system? I’d press them for a fix, such as PERHAPS a new xmitter. (I only say that because they suggested to me that a xmitter COULD be the issue, but rarely) I’ve had no issues with them regarding sensors. they even sent me a sensor that I didn’t ask for and I can’t remember the reason for my call. I can’t remember, because it made no sense at the time that they’d offer a free sensor. go figure. Anyway, try removing the xmitter, clean it, connect it back up to the sensor. The only time I get ??? is on/after day 9. I’ve not gone beyond 12 days with any sensor, so far, but I’m new at this. started in Sept.