Mint Condition FM Synth. Operates on AA Batteries or with the included DC adapter. Has internal speakers and a headphone jack so you can use it as a stand-alone instrument or as a midi keyboard.
https://www.long-mcquade.com/67071/Keyboards/Synthesizers/Yamaha/Reface_DX_37_Mini_Key_FM_Synthesizer.htm
Keywords: Synth, Synthesizer, Keyboard, Mini, Portable, Travel, Piano, MIDI