A sensor-transmitter (20) intended to be fastened to a mobile structure (11, 13, 14) and to transmit a security signal in a home automation installation (10), comprising, in a casing (22, 23): an autonomous power source (36), a vibration sensor (33), a wireless transmitter (35) and a processing logic unit (34) analyzing the signals obtained from the vibration sensor to decide whether to transmit the security signal by the wireless transmitter, which comprises means (27, 32) of detecting the mechanical state of the casing, the sensor-transmitter being: in an operational state when the casing is closed and fastened to the mobile structure, the transmission of a security signal being enabled in this operational state, and in a disabled state otherwise, the transmission of a security signal being prohibited in this disabled state, whereas the transmission of other signals remains possible, or the transmission of a security signal being enabled in this disabled state, the security signal being disabled by a disabling signal.