Is there a such thing as a small mobile device that rings or lights up when another device's button is clicked?

I'm looking for some sort of contraption of some sorts but I don't know what it's called: it's a small two-piece device. One piece has a button and either a speaker or a light on it, the other piece has the same. when one button is clicked, the other piece's light or speaker will flash or ring, and vice versa. It's kind of like the Walkie Talkie with its "CALL" button only minus the large size of it, the wireless connection goes farther, and minus being able to talk on it. Please help. I'm trying to find something like this so I can put it in a necklace or a bracelet for me and my girlfriend so we can call each other in emergencies... Thank you guys in advance.