Years ago I had a bike (CB550K ?) that had an under seat hook to hold a helmet. It's always bugged me that my state of the art Yamaha doesn't provide a helmet lock solution when I don't have the bags on- which is about 75% of my riding. So I came up with my own:
The bracket is made from a piece of stainless steel hose clamp bent to fit as shown. I mounted it under the seat latch nut and put a drop of Loctite on the screw threads. Also put a little section of moleskin on the bracket to prevent any possible seat chafing. The seat pans keep the bracket closed when in use. Both seats are easily removed and installed in usual fashion. It looks flimsy, but is actually quite sturdy and easy to use.
Mission accomplished!
When I do need to lock two helmets(rarely) I pull out the Kryptonite lock from under the rear seat.
The bracket is made from a piece of stainless steel hose clamp bent to fit as shown. I mounted it under the seat latch nut and put a drop of Loctite on the screw threads. Also put a little section of moleskin on the bracket to prevent any possible seat chafing. The seat pans keep the bracket closed when in use. Both seats are easily removed and installed in usual fashion. It looks flimsy, but is actually quite sturdy and easy to use.
Mission accomplished!
When I do need to lock two helmets(rarely) I pull out the Kryptonite lock from under the rear seat.