Help me design a burglar alarm based on light diode

[rithwik]

can some one help me out to do burglar alarm?
i wan thinkin of th light diode .i don remember exactly which diode.the diode has low resistance whn light falls on it.so i was thinkin of buildin a circuit with this diode.was thinkin of emmitub lazer light to this diode . n whn some one passes th light will stop emmitin n th resistance goes high.n th burglar will switch on...can some one help me out with this

 

[Fworg64]

im sure this isnt the only one but there is a part called the DS2E-S-DC5V and what it is is a 2 Form C relay that requires a certain voltage and current to flow through it so it runs, What i would do is this