A wireless button is easier to place when its transmitter does not need a battery. Here, pressing the button supplies the energy: a spring mechanism transfers the motion to a coil, briefly powering the transmission.

The receiver still needs a 3.3V supply. It exposes both a PLS output that pulses for a press and a TOG output that changes and holds its logic state until the next press.

Those two outputs suit different interactions, such as waking a controller or toggling a function. A demonstration test shows operation over a couple of meters.

Documentation: https://www.questwiseventures.com/products/energy-harvesting-wireless-transmitter-receiver