Circuit Alarm for Power Failure Indicator?

Er, an electromagnetic relay, wired as self-sustaining, will do this.

The power source comes from inside the computer (is there something on an USB poer that will do this?). A push-button energises the relay, which holds itself on via one of its own normally-open contacts wired in parallel to the relay.

The alarm circuit is wired via one of the normally-closed contacts.

If the relay de-energises through power failure, the alarm sounds on the power coming on again until the relay is re-energised by pressing the pushbutton.

Simple.

... or for an alarm that sounds when the power is turned off, relay fed from USB +5v out (see pinouts.ru), with alarm connected to battery via NC relay contacts. 5V goes - relay drops out - NC contacts make - alarm sounds. Lots of cheap'n'cheerful piezo-electric sounders available.

Or simpler still buy a plug in power alarm.

I've used these many times for medical instruments which have to be left on and an alarm must be sounded if they are turned off...

You buy them for a few quid (£) and wire it on instead of the mains plug. Then if the computer is turned off or the power is switched off the alarm in the plug sounds...

John.

Buy an UPS. Besides keeping your computer working during a blackout or a brownout, the UPS will sound an unpleasant beeping that can be heard more than a few feet away.

Here you are, you asked for it:

My office power line is on the same wire line with my kitchen. For saving the world from pollution (and saving a lot of bucks), during the summer, I installed an individual air conditioning unit, 5600 BTU, just good for my office and the two kattles (read desktops) boiling on my desk. When my wife turns on the microwave oven in the kitchen, my 20 A breaker trips off and the bloody UPS start beeping. I go in the back yard to the distribution panel, I notice that I've forgotten to take the key from the panel, I go back and get the key, back to the panel, reset the breaker and then, and only then, the beeping stops.

Is this answering your question?

A really good UPS will have programming shipped with it so that it will keep your computer running for sufficient time to be shutdown and secured in the off condition automatically.

You need a if/then program downloaded to your computer with an alternate power source being activated when power is cut. A power circuit board made to gate power can do this. But only with a program to match. Check out power boards for computers. There are circuit boards made for this purpose based on 110 WVolts. Radio Shack would have simullar books on this, "Electronic symbols & circuits". Sincerly,

Keith_moc@yahoo.com

Most new computer will keep +5VSB on USB and keyboard to allow waking up or switching on the computer. So no alarm will sound unless PC is unplugged. Instead use this circuit on internal 5V or 12V.

This is 2 problems: PC turn off and no utility power (unplugged/power failure).