Bought a bluetooth keyboard (Logitech K480), so I can use my tablet during travels. However, it would not connect to my Debian desktop computer. Turns out the formidable Archlinux page on Bluetooth has the solution. You just want to type:

hciconfig hci0 sspmode 0

and suddenly the PIN dialog will pop up that makes everything work… Easy…

By the way, the keyboard is nice and can connect to three different devices. It is just heavier than I would have expected (800 gramms or so).