Safety Grenades, why not in RL? Options

[Riley37]

Advanced option for grenades:
a device built into a grenade fuse which prevents detonation as long as it's receiving a certain signal,
used in combination with a device which emits that signal at strength 0.

Advantage: while the broadcaster is live, your grenades will not go off within 3 meters of you (or any teammate who's also wearing an emitter) even if fumbled or you're KO'd mid-throw or or enemy mage uses Magic Fingers or whatever.

Disadvantages:
1. only works while you're broadcasting, which has negative consequences in certain areas (eg places in which opposition is scanning, and will notice that signal among however many minor broadcasters are active).
2. if the opposition figures out, they can broadcast the safety signal, at whatever power. Or they can jam.
Countermeasure to disadvantage 2: you're scanning for the same signal at any strength higher than 0, and you can reprogram the safety code with trivial ease.
3. Cost. Seems to me this should be relatively cheap, even with enough miniaturization to fit into a grenade.
4. If for some reason you *want* to detonate a grenade within 3 meters of yourself, you need to turn off the emitter.