I bought these for each wheel and the seat post. They replace the bolt or the quick release hub with a spindle that has its own secure nut which in turn has a little magnet inside it which you need a special key to extract, and then you can just use your Allen key to remove the wheel. I carry a little Topeak toolset with me always. Careful not to tighten the nut too much (like I did first time - necessitating getting another having stripped the threads). Available from Hexlox.com.
