driving a 5 volt relay w cortex signal

Recently had a need to turn on a 12 volt siren using the vex ultrasonics as intruder sensors. Had to use 12v for siren so it required a battery w more voltage than vex 7.4 v. Got it to work but had to resolve few issues with probs from vex digital signal only rising to about 3.3 v DC. This is a handy circuit if you want to control something like a 120 v light from a cortex. If you want to know more, post a question here.