The best anti-burglary plan has two main components:
1 - the boat must be hard to break into
2 - it must be apparent to all that the boat is hard to break into
For #1 - I'm shocked how many people haven't upgraded the factory-supplied itty-bitty lock on often-flimsy
companionway hatchboards. This is OK for when you're always within a patrolled marina or club... but hardly enough for
anchoring anywhere in the world. You need a
companionway door that can't easily be picked, jimmied or kicked in. And it should look impregnable. Bonus points if you can lock it from inside.
#2 - One of the most important components of a home alarm system is the little sign on your lawn
Anything you can do to make it look like the boat is better protected will help. Stickers or signs are not as helpful on a boat; a real or fake video
camera with a blinky red LED is better. I would put IR motion-detectors covering the
cockpit and front
deck, that light some serious lights whenever motion is detected on
deck. That alerts the intruder that you're not just whistling Dixie, and they get to see your serious locks more clearly. Also, the light going on/off at night will draw attention.
Finally, if someone manages to enter the
cabin, a dependable trigger like a doorswitch or pressure-mat switch would fire off the alarm, and the most disturbing, disorienting soundmaker should be inside the
cabin. A strobe light is nice too.
Beyond this... not much else possible besides providing an alert via cell-phone that a break-in is in progress. Cameras will
record the event and will be decisive in identifying the thief/thieves.