Instructables user andrewwayneisbored wanted the option to use his headphones either wired or wireless, but he didn't want to spend lots of money on fancy Bluetooth headphones. So he took a pair of over-ear headphones he picked up at the markets, popped open the sides and went to work.
Using this tiny Bluetooth receiver from Amazon, he opened the sides of the closed-ear headphones, installed the receiver and handled the wiring himself (he includes a wiring diagram in the Instructables post so you can see how he did it). It took some effort, but the whole thing was done in one afternoon.
The finished product definitely looks like an old pair of cans, but they're actually Bluetooth-enabled, can be turned on and off to preserve battery life, and they can switch to wired mode when wireless audio isn't necessary. If you're looking for a wireless alternative to some of the awesome headphones and earbuds we've covered before, this DIY option might be right up your alley.
DIY 70's Style Headphone Bluetooth Modification [Instructables]