I got Eircom Phonewatch installed free of charge a couple of years ago .
The deal at the time was that I signed a three year deal. I pay Euro 42 a month.
It is obviously run over the Eircom phone line, but, within the house it is totally wireless and the sensors are not ugly or intrusive. The installation technician was very efficient and installed as many sensors as we felt we needed.
I know people have had frustrations with Eircom, but, I have found them very reliable for this as well as my business broadband (albeit be through Magnet) for my home office. Compared to Chorus and NTL, they are saints!
As I discovered during a Saturday brunch fry-up recently, there is also a smoke alarm which goes off and was responded to by a phone call from the montoring centre.... even though the alarm was deactivated.