Super loud security alarm

Step 5 Add a speaker

Now we need a speaker. If you just use a 8ohm speaker for TESTING, that's fine, but it will definitely not be loud enough to use as an alarm! You'll need a louder output device, like a battery-powered amplifier. I have one that I've used for previous projects; it's from radioshack and I think it costs about $8. You can even make one if you have the parts; there are PLENTY of audio amplifiers here on instructables. The amp pictured here says the power output is 200mw. When I turn it up even 1/3 of the way, and the alarm sounds with it connected, you can hear it from outside the house!

When you connect the speaker to the audio portion of the DIY alarm, polarity doesn't matter.