I'm using a 110VAC industrial signal bell, like a fire alarm bell, controlled by a 555 timing circuit of my own design. The bell is isolated from the timer through two relays. The first relay switches 12VDC to the second relay, which switches 110VAC to the bell. The problem is the timer circuit is re-triggered indefinitely by EMF or other type of noise from the bell. It could be line noise passing through the relays, or EMF released inside the aluminum enclosure. The bell is physically located 6 feet from the enclosure. I've tried other AC loads, such as a high power fan that do not cause this. The AC bell is just very aggressive. I would appreciated any suggestions to isolate the EMF from the timer circuit. Could an AC line filter be used at the entry point of the bell receptacle to the enclosure? I'm not familiar with AC line filters, and I don't want to degrade the performance of the bell.