Some of the Dragon 1/18 german figures came with a tellermine anti tank mine accessory. I glued a mine onto the 'play' button of a digital keychain (this is a keychain that you can record brief reminder messages on). I recorded the sound of an explosion onto the keychain.
I then took a piece of foam about 1 inch thick and hollowed a small section of the underside in the shape of the keychain, making sure to leave a little bit of foam on the topside (ie the hollowed out section does not go all the way through).
Then i just taped the keychain/mine combination in the hollowed out section and flipped it over. You can then drive a vehicle over the foam and if the wheels or tracks go over top of where the mine is the weight will compress the foam a bit, push down on the mine, which in turn presses the play button of the keychain and the explosion sound is heard.
You could paint the foam earth colour, put little shrubs, debris etc on it to make it look more realistic.
No flame or smoke yet...
