Conclusion: we recommend...
If you're out at work during the day but would like to know if your alarm has been activated, a Speech or GSM Dialler that calls you or a nominated person is a good option. You pay a one off fee for the dialler unit and then just for the calls if it is activated.
A more modern version of a dialler system is self-monitoring which uses your broadband connection (or 3G networks) to communicate with you via a secure smartphone app. With camera PIRs installed a self monitored alarm system can even send you visual verification in the event of an activation.
If you would like the police to attend when your alarm is activated, the minimum option is a Digicom monitored system maintained by a recognised alarm company. Remember you will have to pay an annual monitoring subscription and maintenance fee to the alarm co.
For extra security, the Single path signalling system notifies you if the signalling path is tampered with. Again, there's an annual subscription and maintenance fee.
For a very secure signalling device that complies with stringent insurance requirements, Dual path signalling is the choice for you. Pick a system that works with the communication channels available on the premises.
Whatever system you decide on, make sure that it complies with your home insurance company's requirements, if applicable. You may even get a discount on your insurance premium too, so it's certainly a good idea to phone them and check this before you commit to buy a specific system.
« Self-monitored Alarms Part 4