-one safety switch, toggle or otherwise, with on/off (for convinience)
-a pringles can (can be one of the snack size or larger type, i cut down a larger type one)
-a camera flash circuit
-various bits of wire, in total not even a foot, but it's good to have extra.
-a motion/impact switch (i jerry rigged one up out of a grommet, a wire nail, and a bit of wire and solder)
-AA battery holder case thing
soldering iron or pencil
knife or scissors
pliers (or your hands, doesn't really matter)
Step 1: Remove circuit, attach safety
Once you have your circuit discharged, you can begin work.
First switch is the safety switch.
Take your toggle switch and one end of the battery holder, preferrably the forked end (+ end) and solder one contact of the switch onto it by a bit of wire. then, attach the other contact to your battery ( i don't know how smart or dumb this was, as i soldered it in place.) The battery didn't do anything to me, it didn't explode, but in hindsight, i assume this was an unsafe decision. Attach the battery to the wire with elecrical tape or solder a proper battery holder to the original contacts. This creates a safety switch which allows you to cut off power to the grenade so it doesn't accidentally charge and go off, as these circuits are finnicky.
Now take your knife and cut out a hole in the side of your container to fit the switch out the side.
Step 2: Add motion/impact switch, cram in da can!
Now comes the tricky part. You have to get the whole deal inside the pringles can, which can take a lot of tweaking. Once you have it in, the OTHER tricky part rears its head. You have to get the motion switch to work properly by taking the wire nail, and threading it through your grommet so that it doesn't touch it, but will if vibrated enough. this took doing, but i found a spot that works. You'll get it with a bit of tweaking and wire twisting and bending.
Also make sure that your circuit is not completely loose in the can. wad up some duct tape or do something so that it doesn't shake loose every time you drop it. It should be a firm fit when you're done.
Now it is time to test your grenade. Turn the safety switch to ON, take off the cap to your pringles can, and push the charge button on your circuit. Wait for the LED to come on, and turn the safety to "OFF" (you can leave it to ON as a booby trap that when your victim goes to pick it up it flashes again, as well) Then lob in a gentle arc. the flash should go off.
These have practical uses in paintball, and airsoft that i can see.
Note that this is a first design and has its bugs. Fiddling may be necessary. If you come up with an improvement upon my design, give me a mail at firstname.lastname@example.org. Thanks!