Serves as a calling device in the telephones, as an enunciator in the alarm devices, and as a microphone or a telephone in the communication facilities. Manufactured in two variants: : radio installation  840.000 (3000 Ohm) and radio installation 840.000-01 (600 Ohm).

Technical data
Impedance at the 1000 Hz frequency , no less Ohm
-ΠΛ3.840.000;
-ΠΛ3.840.000-01
2400
300
Level of the sound pressure of the calling signal radio installation (ΠΛΗ) 840.000, dB no less than the than frequency of 1100-2500 Hz: 80 dB;
the frequency 500 Hz: 65dB
Average output at the frequency range of 300- 3000 Hz, ΠΛΗ. 840.000-01, Pa, no less than 18. 18
Dimensions , mm Ζ51x30
Weight, kg 0,1