alarm timer help please

I was wondering if you could point me in the right direction so I could build a timer that does exactly what the item in the link does please.

**broken link removed**

Basically I have a CCTV digital recorder connected to an alarm that is giving false activations usually when its windy, it is set to activate on video loss. I need a timer that say after 1 or 2 minuites of open circuit then the alarm will activate or if the open circuit goes back to closed circuit before the 1 or 2 mins then the alarm isint activated.

I hope you understand what I am trying to do and hope you can help as well.

It's would be easy enough to do with a simple microcontroller circuit & relay. Since a 9V battery only lasts about a year according to the brochure it's not the most power efficient design (a typical home thermostat with relay can last for years on a set of AA batteries)

thanks any chance of a drawing and component list?