The motion sensor switch circuit can automatically turn on a water sprinkler but you possibly can easily use it as a motion sensor light switch or motion activated alarm too. Before beginning the construction contact your nearest electronics component vendor and procure a readymade box-type Passive Infrared (PIR) Motion Sensor unit.
Such units, packed in a compact enclosure with power input and relay output terminals are widely available.
In prototype, an unbranded (Made in China) PIR Motion sensor with the following specifications are used. A 4-core screened cable can be used for this interconnection. Power the circuit from a regulated 12VDC adaptor/solar power box.
Whenever the PIR module detect movement of a live body its relay output toggles and the switching mosfet (T1) in the circuit is switched to on via resistor R1 and related parts. As as result, the EM relay at the output of T1 is activated and the electric sprinkler gets its supply through the relay (RLY1) contacts. This contacts (or spare contacts) can also be used to activate a high-power warning alarm.
Please note that, here T1 is wired as a mini electronic timer. Even after the PIR relay switched off, output relay (RLY1) remains in on state for a brief duration decided by the worth of timing capacitor C2.