Proximity sensor as the name suggests it gives an output signal(senses) when an object is at a certain distance(proximity) to the sensor. It acts just like an alarm if something comes near to it. READ THE CIRCUIT EXPLANATION TO INNOVATE...

Step 1: Circuit Components:

IR sensor module (or you may make one... its cheaper to built than to buy. I will upload this circuit if needed)
BC547 (NPN transistor)
SPDT Switch
Relay

This circuit is very simple... but effective compared to costly ones!! depends upon your innovative ideas..

Step 2: Circuit Explanation:

The HEART of this circuit is the IR sensor... depending upon the distance adjustment through the potentiometer, the output terminal gives a 4-5V pulse.
This output pulse is generated through comparison of voltage generated by photo diode due to incident IR ray and reference voltage (arbitary voltage set through potentiometer) by comparator(i.e. op-amp LM358N).
Output pulse of the IR module is fed to the NPN transistor (BC547).
BC547 acts like just a switch i.e. when the output pulse comes to the base, the emitter and collector becomes shorted.
Relay operates due to closed circuit formed by BC547 which is normally open till the base isn't excited.

THANKS, if you understood the funda!! you can innovate just connecting the relay to something else example sliding door, switches to automate things other than alarm triggered by proximity!!!