My parents did the thing where they put keyed deadbolts on all of the doors. So when someone wanted to break in they broke the glass on the door, discovered the deadbolt, broke the glass on another door and discovered the deadbolt, then broke the glass on a third door before yet again being foiled by the deadbolt. Then they broke a window and stole our stuff anyway. Apparently they were professional thieves too, since they were hitting half a dozen houses each day while driving through the state. The cops finally caught them when they were pulled over for driving on expired tags or something stupid. They had robbed over 100 homes in two weeks before they were caught.
The only thing the deadbolts did was to make us replace three extra windows.
About 15 years ago, my aunt stopped locking her convertible. She used to, but people would slit the closed top to reach in and unlock the door to look for CDs and such to steal. A few hundred bucks to replace the top was way worse than losing some change and such. Then she switched to a late 90's Miata which had a lockable center storage bin/arm rest.
A buddy of mine did this in his '70 Karmann Ghia, which, even if the door was locked, was easy to break into with a belt through the window that didn't roll all the way. Someone still broke the window and tried to steal the broken cassette deck that was in it. This was in the late '00s, so I'm not even sure what they were going for there. That cassette deck couldn't have been something you'd even readily be able to give away.
Seriously, a dog[1] apparently is a way better security system.
[1] Big dogs are not afraid, thus they sleep at night if not properly trained. Small dogs (especially Yorkshires) are the most bad-ass security system I've encountered. They bark on anything alive that comes into 0.5miles circumference.
In order to gauge the severity of any potential threat, you have to time the barking interval. If it lasts longer than three minutes, there may be armed men outside your door. Or they have to pee. So when you open the door to let them out, the thugs can enter.
Not really. If you're looking for home security, get a terrier. They are high on loyalty and low on fear, so if they are barking, there's probably a non-packmate animal around. Some were bred to chase badgers down into their holes and kill them, after all. They're anything but timid.
Pit Bulls are terriers, and one reason they are so popular for lower-income city-dwellers is the manageable danger they present to unauthorized, non-packmate intruders in their range. You do not burgle a house with a Pit Bull or Staffordshire in it, period. And you think twice or thrice for any other type of dog. The fences, warning signs, food, vets, and boarding are very often cheaper in the long run than professional alarm system monitoring or contents replacement insurance.
The only thing the deadbolts did was to make us replace three extra windows.