Headphones

As the other user said, a Bluetooth transmitter is what you are looking for. But I wouldn't use wireless for piano practice since even a small lag can throw you off your game. I use a long wired headphone for when I practice

I've tried bluetooth transmitters, and they make the sound quality noticeably worse unless you are paying a good amount of money. Instead got that price I think you should just look at good wired headphones. They will be dedicated for your piano and you can occasionally use them for other things as well. I would recommend getting comfortable headphones so you can sure then fit long periods of time without any issue.

I think getting a wireless headphone with wire support would be safer (no latency) and maybe cheaper.

Just FYI, you're likely to get a slight latency when using wireless headphones. That could potentially cause problems when playing.