It's not exactly custom, but at some point in 4E I purchased some grenades with Smartgun + Voice Activation mods, so I could program a few challenge-response things into them - I'd push a button to arm the grenade, whisper a codeword, throw it, then later in the Combat Turn shout the corresponding second codeword if the grenade was still in a good position, after which the grenade would explode at the end of the Combat Turn. No wireless mode means the grenades couldn't be hacked, and unless they happened to know the codeword pair I was using, the enemy couldn't throw the grenade back and activate it.