| 摘要 |
Housings to accommodate sounders and hooters for surveillance systems have walls with sound outlet apertures and an aperture in the attachment side for connection to walls, floors and base surfaces. To prevent these alarm systems from being disabled due to the housing being filled with foam, filtering areas (15) are disposed on the insides of the walls (11) of the housing (1) at a short distance from them and extending over their entire surface, said filtering areas being fixed to contact actuators (14) of switches (13) of the surveillance system. <IMAGE>
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