The risk of SMS signalling is the messages being being delayed or lost, After head aches with subscribers failing to manage sims / credit, network outage, claims of not signalling... it does'nt have a proper a audit trail it so it not really suitable for a security system
With a URN the police attend on a confirmed intruder, however the keyholders are also meant to attend & not solely rely on a police attendance as its prioritised on their work load.
Last month-
1 genuine break in burglars in a factory, they left with £60 of pretty cash before keyholder & police attended
1 rat chewing a cable to produce an alarm & then a tamper within a confirmation window
Both attended by the police.