If there are 2 monitors in the car (e.g. headrest monitors), they must be tuned to send sound from different channels (otherwise, the transmitters will interfere with each other and a buzzing sound will occur). For this, you need wireless headphones that can be set to work at different frequencies. The biggest advantage of these valves over the HP-1 is the automatic shutdown when the signal is lost (with a certain reference).

Wireless headphones

Wireless (IR receiver)
With compact dimensions
Dual channel (A/B) - required as 2 monitors
A source: 2.8 MHz (right), 2.3 MHz (left)
B source: 3.8 MHz (right), 3.2 MHz (left)
Can be folded together (to be placed in the pockets behind the seats)
Automatic switch-off when the signal is lost (you can't "forget" to turn it on)