weedpharma:
If you try to detect power loss by testing the supply you have lost power to the Arduino as well so how do you detect with the Arduino turned off?You need to rethink how you do this.
Weedpharma
When the 5V from power socket drops I planned to use 12V DC from UPS. I don't mind if Arduino restarts at the point of switching or not.
Arduino is powering bunch of sensors, dht22, fire, movement, noise, atmospheric pressure and water + Ethernet shield + 2.8" tft screen. I didn't measure the current drawn, but when I power it all from PCs USB I have no problems in terms of stability. But as I was reading, the power regulator gets hot at 12V, even if there is little current flowing.