There are some aftermarket systems that prevent keyless entry theft. For example, the Autowatch Ghost Immobiliser secures your car from key cloning, hacking and even key theft. The Ghost uses the buttons in your vehicle, like those on the steering wheel, doors and centre console, to allow you to make a unique PIN sequence that must be entered before you can drive your car. There's also an iPhone app that connects to your vehicle and allows you to get in and drive without having to enter the PIN. We recommend faraday bags, too, like the ones in the Top 10 I'll link to below, but these are cheaper solutions because they're far more simple and these bags cost less because after extended use they can fall apart and stop working.

kit.honestjohn.co.uk/top-tens/top-10-signal-blocki.../