Ok. Fair comment regarding defaulting. I've found the option for software reset.
In each instance, the PIRs triggered a normal alarm event rather than a tamper. Each alarm was caused by a different PIR. First two were on a warm day, so I'd assumed it was related to weather. The third alarm was from a PIR on the front of the house, which doesn't get sun, and was on a cool day. All alarms happened after the system had been set Away for approximately 30 minutes.
No unrelated troubles; missing reports or low batteries are being reported.
Mark