Not all cars nor home speakers come with Bluetooth audio built-in, but chances are you've got an auxiliary input and a means of charging a device over USB in both situations. If that's the case, you can add Bluetooth audio easily and cheaply with GOgroove's BlueGate audio receiver.
Many inexpensive Bluetooth audio adaptors don't charge over USB. We don't know why, but USB adaptors tended to demand a premium. The GOgroove Bluegate, on the other hand, costs less than $US30, charges over USB, and plugs into any standard headphone (1/8-inch TRS) port. It even comes with a free coupler in case you need to extend its very short cable.
If you're adding Bluetooth audio to your car, you just need an inexpensive USB car charger to keep the device running strong and an auxiliary port to connect it to your car's audio system. Many newer vehicles provide a power port and the auxiliary input in the little storage compartment between the front seats, allowing you to hide the Bluetooth audio adaptor and pretend it's part of the car.
The GOgroove BlueGate will stream your music no problem, but if you want to make hands-free calls over Bluetooth it's not the device for you. It does not come with a built-in microphone, so be prepared to make calls the old-fashioned way if you decide to purchase one of these receivers.