Alternatively, you could use some kind of amplifier / speaker to simply make it louder (though this would also make it larger). You could even plug it into the audio input on a Personal Soundtrack Shirt to have an Annoyatron that goes wherever you do.
Step 1: What You Need
- 1x Annoyatron
- 2x wires (preferably red and black, but any two wires will do, so long as they're insulated)
- 1x 3.5mm headphone plug (either from an electronics store, or salvaged from dead headphones/speakers/etc)
- Soldering iron and solder, or conductive glue (not pictured)
The wires should be long enough to give you enough cable to go from the microphone or line in socket on the back of your victim's computer to the spot on the back of the case where you intend to hide the annoyatron (using its built-in magnet).
I would recommend using a soldering iron and solder, so long as you have a fine enough tip to get between the other components to where you need to solder, as conductive glue (at least, the stuff I have - linked) takes a while to set, and you need to hold the wires in place while it sets. I used a ColdHeat soldering iron with conical tip.
Step 2: Detach Speaker
You may want to use some insulation tape to cover the exposed ends of these wires, and maybe tape them onto the metal covering the built-in speaker, to keep them out of the way.
Step 3: Attach Wires and Plug
Step 4: Plug in and Hide!
Once you're happy that it's working, plug it in to your victim's computer, and use the magnet to attach it to the back of their computer. Make sure that their microphone/line in port is unmuted, too, or they won't hear anything. The line in port might be a better option than the microphone port, especially if your victim uses the microphone port for an actual microphone (as a non-working microphone might arouse suspicion). You'll also want to tweak the volume of that port so that it'll be audible over their music (or whatever they normally listen to) - but not too loud, as it's most effective if it's audible but not overpowering.
Turn it on, choose a sound, and wait for them to return to their desk and put their headphones on!
This will probably work best on people who use front audio or USB ports for their headphones, as checking the plug will probably be one of the things they'll try when they notice the noises - along with borrowing other people's headphones, ordering/buying new ones, reinstalling sound drivers or even reinstalling their operating system or going after a new soundcard or even computer!