Cellphones in the dungeon

A long time ago, in a 2E game, one of my wizard PCs invented the talk-rock. Each PC or NPC was given one, and it was enchanted to transmit sound if you held it. Basically, a magic walkie-talkie.

This actually solved a real world problem. Most GMs get annoyed when players split up, then act on knowledge about what's happening to the other group. The talk rocks simply make it possible for both groups to generally know what's going on, justifying a rush to help, or a coordinated attack, etc.

I worked out the idea because my PC had a habit of taking ordinary things, and using a few low-level spells, turning them into useful products. For instance, he had a business (using low level wizards) of enchanting small metal rods with Continual Light. These rods were inserted into nice lamps (think living room lamps, not lanterns or torches), and sold as products.

The talk-rock was a similar concept. A spell was cast on a stone, which left a symbol on the stone. If you held the stone, you could hear what was going on around any other stone with the same symbol. We set the spell level high enough to make it permanent, like Continual Light. Even so, the spell wasn't that high, because it didn't do that much.

It's had some handy impact, you could place one as a listening device. Otherwise, it simply justified knowledge that players already had (since they're all sitting there waiting for their turn).