| 摘要 |
A siren 1 is driven by gas from an aerosol container 5, the passage from container to siren being through an expansion chamber 16 and inlet 17, the chamber serving to ensure complete volatisation of the gas and preferably being a jacket around the siren. The alarm is activated by pulling a plug 9, attached to a spoked ring 10, so that the spokes pivot on the edge of aperture 11 an their outer ends push up on the container 5. The spoked ring may be replaced by a springy dome (Figure 4). For use as the head in an electronic article surveillance button, the alarm comprises an outer casing 51 having an apertured end wall 54, aerosol/siren combination 50 and a see-saw arrangement of one or more arms 57 attached to a pin 58 which protrudes through the apertured wall 54. The see-saw arrangement pivots on a ridge in the casing so that if the pin is pulled down (ie out of the casing) the see-saw pivots about one end so that the other pushes the aerosol container upwards and operates the siren. In a security tag the aerosol is small and volatisation is ensured by the provision within the container of a coarse open celled foam plug (66 Figures 6, 7) that restricts the flow of propellant to the exit tube 14. |
