I've had several freezers with "door open" alarms but they've been all been f***ing useless. Door wide open when I'm rearranging stuff? Beep beep bloody beep, yes, thank you, but it's obvious the door's open isn't it? Door half an inch open because one of the drawers isn't quite pushed home? Silence.
Thermometer-based alarms are useless because they routinely go off during the automatic defrost cycle.
The problem with the makers' "door open" alarms are that they work on the hinge side so they're spectacularly inaccurate. What's needed,
*obviously*, is a switch at the opening edge of the door. But it seems to be beyond the wit of the manufacturers to understand that or to put it into practice.I did try making my own "door open" alarm many years ago, using a timer operated by a microswitch stuck on the side of the cabinet with a lever between the cabinet edge and the door seal. I can't remember why but it wasn't very successful, probably not robust enough for a kitchen environment.
I wonder if some sort of magnetic detector might work better - there are, after all, magnets in the door seal. Or perhaps a low-profile keyboard-type switch between the cabinet edge and the seal? Or any other ideas?