The Oxford LidLocker Helmet Bag finally answers the question: how to leave your helmet with your bike without it getting wet, damaged or stolen?
The helmet stays completely protected from the elements at all times. However, the lock (not included) is threaded down a waterproof tube which runs through the visor aperture and out of the bottom of the helmet so that you can lock it to the bike.
Can be used in conjunction with the following Oxford chains & cable locks: Monster, Hardcore XL, Tripwire, Looplock, Patriot, HD Chain, Revolver, Barrier, Lockmate