Vibrating bracelet controlled from cell phone
The basic idea of "Battery + Pager Motor + Microcontroller + Bluetooth" is simple enough to do. There are tons of projects that do the same. Making it into a audio device is significantly harder, but can be done by using a Bluetooth audio device like the XS3868 or SPK-8635-B. Instead of an led, you include the pager motor instead (with a transistor). The rest is done via the app and the cell phone. Either way, it's not a one day project and you will need to dig down to figure out each part, but you have the general idea of it correct.