Ok (at least) three systems, not four:

Quote:
The wiimote has space for several host addresses (at least 3 are known to work) so it can be paired with more than one host (like PC or Wii) and it will try in reverse order to reconnect to the hosts. That is, the last paired host is tried first and so one.

http://wiibrew.org/wiki/Wiimote

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