Wireless signal transmitter and detector

The wireless signal transmitter and detector (20) is incorporated in or attached to a previously installed electrical switch or sensor, e.g. a light switch or sensor and detects the activation of the switch or sensor for providing a corresponding signal. The signal transmitter and detector may have a self-adhesive surface allowing it to be fitted in a hollow space of the switch or sensor, e.g. between a wiper and a switch insert.