What do you do when your speaker dock stops working? You call it a piece of junk, throw it away, and buy another one. But back when audio gear was expensive and repairable, people—or shops at least—needed gear to figure out what was wrong with it.
This one-off 30-pin speaker dock on Etsy is an old Eico 145A Signal Tracer which probably dates back to the early 1960's. A signal tracer is used to check the signal path of through a piece of electronics. Using the signal tracer, you pump a waveform into one end of your device and follow the circuit from node to node with an included probe. If the gear is healthy up to a test point the probe completes the circuit, and the old Eico's speaker makes a sound. When you hit a node where the sound disappears, you've discovered the spot where something's busted.
You can still buy signal tracers these days, but Eico was liquidated in 1999—let's just say the use of test gear like this isn't as prevalent as it used to be. But this enterprising Etsy seller yanked out the Eico 145A's rudimentary speaker, installed a new 3.25-inch driver, a 15-watt amplifier, and slapped a 30-pin connector on top. It's nice to see the signal tracer repurposed after its obsolescence. Too bad it'll be obsolete again when Apple (probably) replaces its 30-pin connector with something else next month. [Etsy via Reddit]