If you need a simple Time Delay Alarm Circuit, this might be just what you need. Nice thing about it is that since it is based around a 4060 14 stage ripple counter which means there is no programming needed, just wire all of the components and power it up. The circuit uses a photo resistor to start the timer, the circuit wants to be in the dark, as soon as it is moved into the light the timer starts and if it is still in the light after 20 seconds the piezo buzzer will sound. This circuit could be easily adapted to monitor almost anything by replacing R2 with a switch, for example if you mounted a N/O (normally open) switch on your front door you could be notified when your front door has been left open for more than 20 seconds.
For full build details check out DIY Electronic Projects.