By reading different values from the sensor, we can detect if is it light , dark or a value between them. Another element that we are going to use on this experiment is Piezo Buzzer. So what is it ?

Here is an ultra simple Arduino Night Alarm project wired around a handful of inexpensive and easily available components. One advantage of using Arduino as a security system is the flexibility!

Once you get the alarm set up, it’ll sense movement near the Arduino, snap a picture, then send it over to you using If This Then That. All you’ll need is an Arduino Yún, PIR sensor, a USB ...

To alleviate concerns of burglary they rigged up a proximity sensor to an Arduino Diamondback setup.

The alarm/target works using a piezoelectric sensor attached to the clock’s housing. When the alarm sounds, if it senses a dart hit by counting the signal pulses generated, it turns off.