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Door open timer switch thingymajig

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zpyder:
Hi all, here's an interesting electronics project/problem.

At work we have a desiccating cabinet that is used for drying filter papers and things out. Our technicians have a bad habit of leaving the door open, or unlatched, resulting in normal air getting into the cabinet and so the stuff that's meant to be dry ends up with some residual moisture.

I built a simple buzzer alarm that would sound whenever the door was open. Was just a buzzer, 9V battery, and a magnet reed switch on the door. The issue was that the proximity required for the reed to switch states meant that the buzzer wouldn't sound if the door was pushed closed and not latched - which isn't acceptable.

I'm now wanting to build a buzzer V2.0, with improved functions:

* Time delay so that the door can be opened, something put in/taken out, and closed, without the buzzer going
* Sensitive enough that the door absolutely has to be closed for the buzzer to not go off. The slightest crack is not good

If anyone has any recommendations that'd be good. Cheapest, simplest option is preferred, I'd love to do a raspberry pi thing but I think that's overcomplicating it. I'd also love to be able to say to the technicians to make sure the door is closed and for them to actually do it, but that's never going to happen either...

XEntity:
Use an ESP8266, such as the Wemos D1 Mini, you can power from USB, costs about £2-3 and will run Arduino code programmed direct from the Ardunio IDE, can attach a piezo speaker, if you want to internet connect then has wifi, has multiple IO so you can connect reed switches/ ultrasonics / hall sensors.. whatever you like and will simply do timed delay without the overkill of a Pi..

zpyder:
I decided to get an arduino starter kit so I can just have fun learning the whole ropes. Was the equivalent of £30 from the nz equivalent of maplin. Having fun so far :D

XEntity:
Cool basically if you get something working, I’d recommend still running it from an ESP just because they are smaller, cheaper and usually more powerful.. if you need any help let me know

Serious:
 Obvious answer would be an automatic closer, same as on fire doors, problem is some idiots tend to put things in the way to stop the door closing.

FRIDGGI actually produce a fridge open alarm, exactly what you are trying to make, for about £20, bound to be other options.

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