When we purchased our home 4 months ago, it was prewired for Brinks Home Security. We decided to active it and have so far been happy with the service. We have all three exterior doors monitored along with all windows. We opted against the motion detector and sound detector since we have dogs in the house.
For when you leave, you have 40 second delay to exit and a 20 second delay to enter. However, the one feature I liked most about this system is the instant alarm button. At night, we can set the alarm to instant so the alarm will sound the second one of the 2 front doors is opened (the back door and all windows are always on instant when the alarm is set).
The alarm is very loud. We have tripped the alarm a few times already and I would think it would definitely scare someone away. Within seconds, a representative from Brinks will call to check on you. They are very friendly, even at 5:00 in the morning! Once they have confirmed your password with you, you know they will not call the police. However, if you don't answer the phone, give the incorrect password, or give the wrong code they will call the police.
Sometimes I think the price is a little high. We have had another reliable security company and the price was cheaper. However, since the home was prewired for Brinks, we had no choice but go with Brinks unless we wanted another system installed. I am happy with the service though and I feel better knowing my house is monitored.