Thanks to the wonderful ToothFairy I am able to conveniently share an Apple Magic Trackpad between three MacBooks! These are normally used as mobile devices, but when working at the desk a separate keyboard and trackpad are preferred. I already got a Bluetooth keyboard, a Logitech K760, that can be paired with three devices and has three dedicated keys to switch between them. Now I had to find a way how to accomplish the same with my Magic Trackpad.
As it turns out, the Apple Magic Trackpad is able to be paired with multiple computers (and possibly iPads) and will remember these pairings. It can — however and of course — only be connected to a single one at the same time and will automatically connect to the last one used, and when connected it does no longer present itself for pairing. So in order to be able to pair it with another computer, just turn Bluetooth off on all the other ones, and the Magic Trackpad will appear in the Bluetooth device list as a newly available device.
After having been paired to all devices, the remaining problem is how to make the trackpad switch between them. As soon as it is connected to one, it will just ignore connection requests coming from the others. So it needs to be disconnected first.
This is where ToothFairy comes in to make this process easy and convenient. I added the trackpad to all computers so that an icon appears in the menu bar which shows the connection state and which can be clicked to connect and disconnect. Of course clicking the icon does not work so well without a pointing device, so I assigned a keyboard shortcut. Whenever I want to work with one of the MacBooks, I connect it to the external monitor and press the dedicated key on my multi-pairable bluetooth keyboard for the respective machine, which will cause the keyboard to establish the Bluetooth connection and wake it up. Then I enter my login password and press Shift+Control-Alt-T to have ToothFairy connect the trackpad. Voilà!
I just wanted to share this here in case someone might find it useful or inspiring.