I recently installed a Yale HSA 6400 alarm system. Everything worked perfectly until I added 2 additional PIRs for the shed and the garage. Now the external siren and Control Unit siren no long sound when the alarm goes off although the system does still send messages to my mobile phone. The tamper alarm still works on the external siren when the cover is removed so the batteries are fine (the system was only installed 2 months ago). I tried 're-learning' the siren but the Control Unit already recognises the siren. The external siren can still be set to Entry Sound On so that it beeps when the alarm is switched on. I tried a walk test and all devices are working perfectly and each causes an alarm when they are triggered it is just that the siren never sounds so the alarm system isn't much use at the moment. Does anyone have any ideas?