Is there a device I can use or mutate such that if my front door is left open for more than a minute an alarm will sound - (people leave it looking shut but with a gap so loads of warm air is lost.) ((My front door is very heavy so I'm not sure a door closer would work in wind)) [g]
A reed switch and a magnet would form the basis of the detection mechanism - especially as you can get made-for-purpose magnets and reeds.
Buzzers and 9V batteries are easy.
So that just leaves the problem of a time delay. I would use a 555 timer chip on a bit of veroboard, but if that scares you - I'm not sure what to suggest - maybe someone else can think of something?
You want a fridge alarm - or similar. Try
This came up a few weeks ago. I have the one with the variable delay and it would do the job perfectly, but it's a bit bulky and wouldn't look very nice on a front door
A wall-wart power supply, and a "time-delay on" relay would do the trick to complete your circuit if the OP doesn't want to get down to component level.
SteveW
Thermostat feeding electric bell (and wires to croc clips to apply to miscreants.....)
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