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The hearing aid AK-1 (581M) was produced presumably since 1965 by the Moscow hearing aid plant. It is used to compensate for small, large and medium hearing losses due to air or bone conduction. It can work with power from one or two batteries, which respectively provides a maximum acoustic gain of 60 and 128 dB. It has a smooth volume control and a four-stage tone control. The plant produced two models: AK-1B, equipped with an air conduction telephone, and AK-1K model, equipped with a bone conduction telephone. The device is adapted for telephone conversations and eliminates the effects of external noise. The dimensions of the device are 66x44x15 mm, the mass with two batteries is 75 gr. Presumably, since 1978, the plant produced an upgraded AK-1 device (VM or KM), characterized by the transfer of the circuit from germanium to silicon transistors and, accordingly, more modern elemental base.