This particular unit has an alarm that can't be turned off.
As far as the possibility of false readings goes, the readings were consistent for an hour and a half ride. And it was 76 degrees here today, so I don't think the cold was a factor.
I guess it's going back and I'll try a different one. I'm still concerned about my elevated heart rate readings though. I can't possibly be training to hard if I'm averaging 15mph and my perceived exertion is moderate at best, but after searching this forum and others it's clear that I shouldn't be seeing 170+ bpm without some pretty serious effort either.
Az