This is the PowerPlay PM1 Personal Monitor In-Ear Headphone Amplifier Belt Pack.
Whether you’re a keyboardist, drummer, or any other musician whose performance keeps them anchored in one spot, the PM1 was designed specifically for you. A convenient hardwired personal in-ear control center, the PM1’s belt pack puts monitor control right at your fingertips, plus it’s lightweight, ultra-easy to use – and it doesn’t require a power source!
The PM1 features an extremely high-quality volume control for dialing in the perfect level every time. Designed for long life and super-smooth performance, this detented control stays where you put it.