I am looking to add a power outage alarm to my 5v Arduino Uno. The alarm will be powered off a second 12v transformer that will sound if the Arduino loses power. I was originally thinking of using the same electromechanical relay that I am using to switch some 120V loads http://pewa.panasonic.com/assets/pcsd/catalog/js-catalog.pdf
I was thinking of wiring the alarm to the NC contact, then holding the contacts open while there is power, so when power falls out, the circuit will close. I then saw some 555 timer ICs that look pretty good, except that the alarm voltage has to be equal or less than the microcontroller voltage, so this wouldn't work.
Should I go with the electromagnetic relays, or would the 555 be a better option (if I can use 12v alarm)? I thought of using a latching relay, but there wouldn't be power to unlatch it during an outage, correct?
Thanks in advance!