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 ...

As photons (light) land on the detector, the resistance will decrease. The more light is we will have a lower resistance. By reading different values from the sensor, we can detect if is it light , ...