I've got 2 remote PCs, one that runs on a power backup and one that's connected directly to the electricity.
I just want to be notified when there is a power failure, so the pic needs to be connected to the "power backup pc" and when the power drop, it must send something to the PC via RS232 and the PC must send me an SMS or email.
I will run the PIC from battery, but how do I easily detect when the power drops?

Thank you!