I have an idea to make an alarm that turns my room light on and off in the mornings to wake me up smoother. I was thinking that I take the positive end from the beeper on one of my alarm clocks, and wiring it the base end of a transistor, with the collector/emitter bridging my light switch. Do transistors have a max voltage rating? Can i use any npn transistor? (i think i would need npn) thanks
No dont do that, your transistor will be vaporized as soon as you apply power. Most transistors can't handle line voltages. you need a triac circuit that uses an optoisolator.
A triac can handle AC line voltages and the optoisolator will isolate the line voltage from your alarm clock.