Disc locks and in-built immobilisers
Your bikes immobiliser and steering lock dont do much. Thieves tend to know how to get past these easily enough. A disc lock is compact, easily transported and makes your bike marginally more trouble to nick. But most bikes can be lifted by two blokes and shoved in a van. Theyll have the disc lock off with a cold chisel in seconds. And the feeble alarms fitted to most disc locks are barely worth it. Plus theres always the risk of trying to ride off with it attached. A lanyard or warning device will help (when used) and train yourself to never put the key in the ignition until you remove the lock.
Once all the rage, few are fitted now. People often ignore them and theyve caused many a roadside stranding. In fairness, failures were often down to poor DIY installation. Though even the best systems went wrong as they aged. Modern alarms are more reliable but choose a top system, approved and fitted by the dealership, and with a long warranty.
Simple but effective, chaining your bike to something immovable should prevent it being taken. Route it through the frame or similar and not round an easily unbolted wheel.
Choose a chain with a Sold Secure rating. The best are thick, toughened steel over 19 mm thick (so it wont fit in the jaws of standard bolt cutters). The steel should be hex or square section, round is easier to cut. Links should be covered to prevent damage and for extra security.
If you can, keep chains off the ground to hinder leverage.
On the move, youll need a lighter chain you can keep with you. Again, look for Sold Secure or similar ratings.
At home, chain your bike to a good ground anchor. Set it in reinforced concrete or screw in using non-removable bolts (for example with steel-ball inserts).