You know this problem - you've got a home with more than two rooms and you need to figure out how to play Lasertag in it - but there's no way to mark the spawn room!
I know, happens to me all the time.

But fear no more, as the IR Bacon is now officially (not) out!
Be amazed as you plonk this tiny, very cheap and simple to make circuit onto your table, slap a battery on it, and irradiate yourself with gorgeous 850nm electromagnetic radiation! 
The IR signals sent from this device spread through your averagely-sized room, while not bothering anyone on the outside, allowing for room-precise locating beacons to be used for things like my Lasertag project or other things.

Locating beacons aren't your thing?
That's fine too. These little fellas include a broken out I2C and GPIO connection, making them the perfect candidate for low-power Smart Home sensors (as long as transmission reliability is no concern ;) )

Even better yet, they also feature three WS2812 LEDs to display various information, a single button (!) for user-input, and a buzzer to beep around in various (i.e. more than two!) frequencies.

So far these things have already proven themselves to be mediocre:

• Locating beacons (as described above)
• Quizz-Buzzers for small-scale crow control and general student lecture shenanigans
• "Simon-Says" buttons

Tag along to see what else I can cram into these little biscuits!