Daniel Spalding
Hi With regard to contact or shock sensors. I suppose vibration because if an intruder smashes the glass and doesn't open the window then the alarm will still activate, although most shock sensors come with a built in contact which i like because if you forget to close the window when you go out the alarm will notify you. PTSN vs GSM i suppose GSM is more secure if like most your telephone cable is exposed on entry into your pemises. Regards Dan isecurityplus.co.uk
