The acoustic signalling device HEROLD-3 is equipment for mining machines and is meant for emission acoustic warning signals prior to starting up the machine and also for emitting predefined information signals. The emitted signals meet requirements set by Polish standard PN-G-47050. On request, we can implement any other type of signal. Construction of signalling device meet requirements set by standard EN 60079 and adapted to be mounted in a flameproof housing. The device has an autonomous, intrinsically safe power source that is recharged during operation of mining machine.