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Based on your description, it sounds like there is a run of alarm cable parallel to the lighting circuit. If it's a basic alarm panel with a global tamper circuit, you'll see a spike coupled in when something like a fluorescent tube strikes as the panel has high impedance inputs. One solution would be to get a ferrite core and wind a few turns of two tamper wires going into the tamper circuit around the core. The windings must be in the same direction and same number of turns and this'll give you some common mode rejection (which is what you'll see from the parallel run). Otherwise you can probably use that off-the-shelf suppressor, or even better would be to move the alarm cable away from the mains circuit. It's highly unlikely this is anything to do with the AC supply to the panel as it would not meet EMC regulations if this was the case and there is heavy capacitance around the voltage regulators anyway, so HF spikes won't make their way through.