I work in an educational program that is set outside the normal high school campus. Since we're in essentially an office building without the typical amenities of a school, we don't have bells to warn for classes ending or beginning. The students we teach are not mainstreamed, but we feel that adding the typical school bells might aid in the path to reintegration, getting them used to the timed schedule reminders, but also to keep the three separate classes in sync better, instead of having some kids get out earlier and barging into their next class, interrupting everything (a frequent occurrence).
An apology first. The pictures are not very good. They are mostly quite blurry. I took them with a Photosmart E327, one of the worst digicams I've ever used. It's what the school IT people picked out because I was too busy to put decent effort in picking a better low price option. I also kept forgetting my coolpix 995 at home. There's really no details that are required though, so the pictures are more for visual appeal and reference... oh, and some proof of the cool cannibalization I did for the project.
Not having to spend any money was an important part as well. Having the luxury of an older unused laptop made a significant difference and a warehouse of old computers to pillage helped too.
Step 1: Tools
Screw drivers (flat and philips head, better to have both when you don't know for sure than to only have one and need the other)
Wire stripper or wire cutter, pliers and a steady hand.
Sharp hobby blade
For the most part, I used my mini multi-tool.