We've had one for many years. They won't stop a burglar if they want something from inside "my" house, but for an "any house will do" quick burglary, they will move to a house that has less chance of making a noise and draw attention, or unlikely to be connected to a control room who can quickly send someone around. That is straight from the mouth of the police who used to come to our neighbourhood watch meetings.
So, they have their uses, and I like to know when I enter the house that there is nobody inside, which happened to a friend once.
For a rental, I'd not bother. In the house we had an alarm system, not one tenant kept it up. They didn't see any value in it.