The MH that we have was fitted with a Linnepe Sopoalarm when we bought it. Has anyone else one of these fitted as I'm thinking of removing it as we don't have the on / off key. Its simple enough to replace the key switch but I'm not sure of the units use really as I don't think I believe in the 'gas attacks' too much! The only thing that stays my hand is the mention in the manual that other sensor heads can be fitted and I just wondered if anyone has these or know of them and if so what do they think please?