What is a GSM Alarm Dialler?

GSM Alarm Diallers are fairly new to the market (i.e. the last 8 years or so) but in that time have shown themselves to be very useful and convenient either as an alternative to a standard Alarm Dialler or as a backup device. In situations where it is not practically or financially viable to get a land line installed or where there is a high chance someone might try to block the line a GSM Dialler can be ideal. A GSM Alarm Dialler is essentially the same as Landline Version but accepts a sim card and uses the GSM networks to make and receive alarm calls rather than PSTN land lines. Not all GSM Diallers are equal most are very cheap and are not designed to cope with commercial or industr.......
What is a GSM Alarm Dialler?