ADT Group
of Sunbury on Thames, subsidiary of a Bermuda-registered company.
1990 ADT UK Ltd became ADT Group Ltd
1996 Tyco International bought Thorn Security for £138million[1]
1997 Tyco International acquired ADT[2]. The Thorn Security business was absorbed into ADT and all but a handful of the famous red 'THORN' bellboxes replaced. However, the Fire products especially are still to be found in many premises and until recently spares and complete systems of Thorn heritage continued to be manufactured by ADT.
ADT Security Systems acquired Modern Security Systems which, together with Thorn Security, formed ADT Fire and Security plc[3]