Phototransistor laser security system

[triflypaul]

I am building a laser security system, I will be using a small laser to energize the phototransistor. The phototransistor will energize when the laser shines on it and it will connect to a transistor base. This should set the transistor in the on position. That part of the circuit I understand, the part I don't get is how do I make a simple switch to activate the alarm when the laser beam is broken and the and the transistor is now in the off position. Please be patient with me the last time I opened a book on electronics was in vocational school in 1970. I am just getting back into it just for fun.