I have an alarm system that I would like to put on a UPS. Problem is the UPS that I've tried aren't very happy on the light load presented by the alarm. The power consumption is virtually zero unless the alarm is sounding. I think this is causing the UPS I have to generate a lot of noise that's messing with the alarm panel. The panel operates from a 220VAC to 9VAC mains adaptor. I've looked at a few options such as increasing the battery capacity in the alarm panel itself and feeding the panel something like 12-13V DC (which should go through it's bridge rectifier) but these introduce other problems. So what I'm looking for ideally is a 12V DC to 220V AC pure sine wave inverter that is stable on loads from 0 to say 50W. Do such things exist as I can't find one that specifically refers to light load operation. An alternative would be a 12V DC to 9VAC pure sine wave inverter.