I've just tested the simulation with clocks sending out alarm pulses as low as 1V peak-to-peak at 500Hz and the resulting reset pulse trains look fine. Good luck with the build. Bear in mind that if the timer range etc is set to 2hrs as per post #21 then manually resetting the timer by pushbutton will give a 2hr timed period, whereas alarm signals lasting 1hr will give a 1hr + 2hr = 3hr timed period. If that's a problem we'll need to rethink the auto-reset circuit. It would help if we knew exactly what sort of signal (voltage, polarity, frequency, duration) is available to you when the alarm sounds.