A glass window pane breaking device comprises a suction pad for attaching the device to the window, in use, a striker rod with a breaker tip, a trigger pawl engagable with the striker rod and a remotely operable trigger which is biased normally to prevent movement of the trigger pawl and thus to retain its engagement with the striker rod when this is held against the force of charged energy storage means urging the breaker tip in a direction to break the window pane, in use. A switch is also provided to ‘arm’ the device or place it in a ‘safe’ mode.