Good quick/simple over voltage solutions?

[XOIIO]

This is something I've begun to wonder about recently, are there any fairly simple DIY over voltage solutions you can rig up yourself without using something like a fuse? I have a replica portal gun I want to add a DC power jack to at some point when I have a display case, rigging up some over voltage protection to cut out if the input went over 4.6 volts would be handy.

If I used an LM317 to do this it would be simpler (and allow a much larger range of power supplies to be hooked up, not precisely the right one), but if there was a smaller solution, I could probably fit it in the battery compartment, and not need to take the whole thing apart which would mean breaking the plastic welds holding the shell on. That would allow for some more customization but I am still having trouble bringing myself to do it. if I did neodymium magnets would probably work fairly well to keep it on, that first step of cutting it off though (and getting a small blade up in there to do it) is something I am squeamish about doing.

I'm guessing there are maybe some small IC's or a small board on ebay that you can program to cut off power if the voltage exceeds a specific amount, just not sure what exactly to search for.

[theatrus]

Zener diode and a PTC/Fuse. PTC first, zener to clamp the voltage.

[Holograph]

Zener diode and a PTC/Fuse. PTC first, zener to clamp the voltage.

This is exactly what I was thinking - assuming the thing isn't drawing a whole lot of current. Is it basically just to run some LED lighting?

[Unixon]

A proper TVS instead of zener would work even better.

[theatrus]

A TVS would be better, as they're designed to absorb more energy in short durations.

http://www.digikey.com/product-search/en/circuit-protection/tvs-diodes/655429

Take your pick!

[SeanB]

PTC fuse, zener diode and crowbar thyristor. Add reverse voltage protection diode as well.