I work for an alarm company as my day gig for the past ten years. I have had two attempted breakins at my house in the past 8 or so months. Actually once they got the door kicked in. In both cases the siren scared the intruder off. In both cases I had signs/stickers prominently displayed. Unless the intruder was illiterate, they knew that i probably had an alarm before they tried their luck. I honestly don't think that just signs/stickers are as an effective deterent as they once were. Too many people just won't use their alarms on a regular basis and burglars have figured that out.
A few of rules of thumb. Wireless systems suck. Avoid like the plague. ADT also really sucks. Avoid like a 300 lb. hooker with the plague and syphillis. ADT lies, will raise their rates constantly and behave in an unscrupulous manner. If you get motion sensors, don't skimp. Get the nicer ones with a large pet immunity. 90% of false alarms come from motion sensors picking up small movements that are not people. Drapes blowing when the air comes on, ceiling fans, even large moths/spiders moving around. Seriously. The extra $40 or $50 bucks for a nicer motion sensor is completely worth it. Glass breakage sensors can cover pretty large areas. Instead of a bazillion window contact or shock sensors a single glass breakage sensor in a central location can sometimes cover a couple rooms if the layout of your house is open enough. If someone cuts your phoneline your alarm won't transmit a signal to the monitoring station unless you have a cell back up unit. A cell back up involves not only an actual unit, but also a recurring monthly fee for a stripped down cell number. A cheaper alternative to the cell back up system is a phone line tamper sensor. If someone cuts your phone line, that sensor sends an alarm to the monitoring station notifying them that the alarm has been cut. This is the only signal it will send, but they should dispatch on that anyway. That being said, I don't have either on my own alarm and have no plans on adding one.
Monitoring is worth it IMHO. You can usually get monitored for $20 or less a month. If you notify your insurance agent that you are monitored they will usually discount your homeowners at least $10 to $15 a month. Do NOT go for a monitoring station unless it is owned/operated by the company who is installing the alarm. Many companies will pay another company to monitor their accounts for them. This just in general is an added level of headache/compexity that is best to avoid. You also want to make sure that the monitoring station is local. If the alarm company is giving you a 1-800 number then it is a good bet that the alarm company is a couple states over. Mega monitoring stations suck. They cover vast areas and are easily overwhelmed if many people trip their alarms at once or during storms. Alarms can sometimes be tripped by nearby lightning strikes.
PM me any other questions that you think of. I'll be happy to answer whatever.
PS: A dog is also a great idea. Preferably something at least 40 lbs or so.
PPS: I can't emphasize the avoid ADT thing enough. Seriously, AVOID THEM!!!!