I'm a bike thief.
Here's what I will do to get your bike...
Type 1: Joyrider.
I will hotwire your bike, screwdriver the ignition or get it going somehow. I will then take your bike for a blast and torch it when I'm done.
I look for: Anything unsecured, usually something fast like a sports bike or, since I'm a 16-year-old scrote, something easy to ride like a 125.
How to stop me: Make the bike immovable, with so much security that it's not worth it. Chain, disclock and perhaps an alarm to scare me off. Immobilisers will slow me down. Covers mean I don't know what your bike is. Trackers may help recover your bike, but you may find a burnt-out wreck by the end of it.
Type 2: Professional thief.
My mates and I will lift your bike into a van, shielded from noise and tracking signals. It will take between 8 and 15 seconds (count that out, right now). I wil then flog it overseas or break it for parts.
I look for: 125s (always a market for those), popular bikes and anything I can break for parts. I don't like unique or heavily customised bikes as they're easily recognised.
How to stop me: You can't, really. Not if I *really* want your bike.
Best you can do is deter me with a combination of securities, hide the bike and make it so much hassle to nick, that we'll go looking for an easier target.
The lowdown:
Chains: Keep the chain WELL OFF the ground (makes using bolt cutters very awkward) and chain it to something immovable like a lamp post. Put the chain through the frame, rather than something that can be removed from the bike (ie the wheel). I'll really need a plasma cutter to get that bitch off!
Immobilisers: Lowers your insurance, but I'm simply lifting the bike up, so that's no use.
Datatag: Marking parts can help as I might be scared of selling stuff on public channels, but who would really ask? Outside of that, I can just flog it at car boot sales and stuff. Cheap and still worth doing, though.
Cover: If I can't see what bike you've got, I probably won't waste time looking.
Disclock: Bit of a bugger. I can still lift the bike, but it's one more hassle.
Alarm: Ah... noise is not good. Draws attention. Plus, it means YOU will know about it and the last thing I need is a pissed-off biker coming at me with a weapon. Ttaskmaster himself can be outside and hurting bike thieves in seconds!!
Security lights or parked somewhere well-lit: Anything that would make my crime easier to see might make me think twice.
Hide the bike: In a secured garage is best. Make sure the door has a lock that prevents the door from being opened. Not the one it came with (I can screwdriver those), but one of those 'doorstop' types that physically prevents the door from opening. Check also that there are no windows or other ways I can easily bash my way in.
Consider also secutity lights and a garage alarm.