Step 4: The Laser
The Dollar store magnetic door chime not only had the slide switch that I wanted, but also it used the same kind and number of batteries that the laser does. This was cheaper than buying just a switch from an electronics supplier.
I removed the tiny circuit board from the door chime and installed the working guts of the laser in its place using the chime's switch and battery holder.
You don't have to go to this extreme if you don't want to. Just use a rubber band rapped around the laser pointer to keep it turned on.
Like the photodiode, I hot-melt glued some magnets on the back.