The BIA (Beltpack IFB Amplifier), battery-powered belt-pack unit, allows either loudspeaker or headphone monitoring of a communication or audio feed, and is typically used with a presenter's earpiece as part of an IFB kit.

The input gain is controlled by a potentiometer, a 0/20dB gain switch and a selectable limiter. The limiter can be used to ensure a safe listening
level over a wide range of input signal levels and also improves signal intelligibility by preventing clipping of the output signal as the battery
discharges. The balanced output stage of the headphone amplifier drives earpieces and headphone, having either mono or stereo jack plugs,
with connections to the tip and ring only .
Although this cause headphones to driven in anti-phase, intelligibility of speak is unaffected, and the higher impedances of the series
connection ensures the most efficient impedance match to the output stage.

BIA is compatible with similar apparatuses of other brands in commerce.