Door open alert project.

Thread Starter


Joined Aug 9, 2011
My project is to sound a short (perhaps 2 second) audible alert when a door is opened up.
And then to reset itself when the door closes.
Again the only time the alert should sound is on the door opening (only 2 second regardless how long the door remains open).
How should I build this?
Should it be 555 or 556 timer based, or 74121 or something else.
And should I use a pezio buzzer for the audible alert.
Thank you
Last edited:


Joined Jul 9, 2011
As I said in the other thread, the door switch must be closed when the door is open and stay open when the door is closed.

It is also possible to do it with a momentarily activated switch (or two) when the door opens, but the circuit is going to be bigger.

The timer is set for 5 seconds, for two seconds you need to adjust the timing capacitor/resistor.