I use a professional local guy (in business 30 years) at $35/mo for a system that monitors more than 30 sensors (doors, windows, motion, heat, smoke) and records a dozen cameras. He lives 10 minutes away and responds instantly to texts or emails to issues or questions. ADT is a ripoff.
But generally all burglar alarm systems are not money well spent as they are too often either (1) setting off false alarms, (2) not set properly to catch the thief, (3) bypassed by the thief, or (4) ignored by the thief and neighbors and police who take ages to respond if they show up at all. In most jurisdictions, police do not respond to burglar alarms without confirmation.
Smoke/fire alarms are a different matter and can be the difference between a $10,000 fire and a total loss.