Pinhead provides locks for headset caps, seatpost clamps, and wheels (both QR and solid axles). They can be purchased as a complete package for all items or you can have add-on pieces keyed to match existing Pinhead locks. These anti-theft device take the place of regular skewers/bolts to prevent opportunistic thieves from swiping you components.
I’ve installed these items on customers’ bikes. They do the job, but for the utmost security make sure you use their newer “POG” washers to foil especially well-prepared criminals. I also recommend that you leave the skewers long rather than cutting them to minimum necessary, because a bit of skewer sticking past the lock face will allow key/wrench to stay in place a little better. Without that, it’s really difficult to crank on the skewer to get it tight enough to hold like a regular QR; the key wants to slip off the lock face. Annoying…very. Pinhead wheel skewers wouldn’t be my choice for a bike with horizontal dropout, though the solid axle lock might hold fine in such a frame.