Specific details vary between alarm companies. But the point in general is that an alarm system is essentially like another phone or fax or answering machine, and it needs a line filter installed in front of it. In these cases we always advise best course of action is to contact your alarm company and find out if a central filter has already been installed and if having ADSL on the line will interfere with their alarm system in anyway. Your alarm company should be able to advise your options from there. Please be 100% clear that we take no responsibility for the correct operation of your alarm system in the presence of ADSL services. This is entirely a matter between you and your alarm system supplier.