Peter_n:
You need 3 AA batteries.
Therefor the sensor should still work at 3V.
If you use a transmitter (switched on once per 5 minutes) it should last for a year.
And lets assign half the current for the sensor.
Suppose AA battery of 1500mAh, I use 1000mAh for safety. One year is 24*365 hours.
Current is 114uA. Half of that is about 60uA.
Perhaps a sensor like the AN48841B or the SL353LT.
okie, I'll look into that. Still need to figure out how to use the counter on the 328, but that's my problem. =)
3AA batts would put me at 4.5V, which is the lowest voltage the 328P at 16Mhz will run at. Wouldn't give me much room for sag. So I'd probably want an 8mhz 328P, Hmm...