Getting back to your question gayathri.
I have phonewatch and the wife is fels safer having it. Instillation price is not bad - the always have a deal running, but its not that cheap in the long run with the monitoring charges and extras for servive options etc.
Works OK so far but dealing with phonewatch is fairly poor - if you have a problem with their service they seem to just say 'we can send you the form to cancel the service' almost straight away.
Instillation costs vary depending on wired, wireless, amount of sensors etc
Monitoring is 250/year
Depends what you are prepared to pay for some peace of mind.