I have worked security in the military for several years. The best defense is to never let theives know when your building is vunerable! Being unpredictable is your best tool against theives. Never post or tell everyone you are going somewhere for a long time, I always let everyone know (excepte a few trusted souls) after I have returned. I vary my schedule as much as possible. I go home during the day at different intervals, take a day off in the middle of the week, etc. If I wake up in the middle of the night I may go outside. You can use timers to turn lights on and off at different times.
As for physical security, it all depends on the construction of your garage. Is it attached to your home or stand alone? What type of material is the outside of the garage made of and what type of doors do you have? HOw is the light around the garage?
Alarms generally deter someone once they are in and will grab and run and potientially cause more damage. Security cameras will only capture what is being recorded and I doubt you are going to sit and watch the monitor all night.
The best thing to do is make it hard as possible to get in the garage so the thieves will go somewhere easier.
Main thing is the door, is it a standard home door with glass and a wood frame? You need a heavy duty steel door with a steel frame that is secured to the slab and structure as good as possible. are there windows in the garage? Can you put cages over them that cannot be tampered with from the outside?
Thieves are like water, they will go with the route of least resistance. If there is someone who knows what you have and wants it, then they will look for things like when no one is home (work, vacation, going out) so they have time.