VEM | DS977

VEM DS977 is the most common mechanical siren in Czechia, and to this date, a siren with the largest count of remaining devices in operation amongs all mechanical sirens in the country. The siren has been frequently exported into the Czech Republic (at the time Czechoslovakia), most likely from the 1950s up to 1990s, presumably as a result of good relations with the GDR (German Democratic Republic), which was the home country of the manufacturer.

This siren is known to have a long wind-up to full speed (approx. 4,5 seconds) compared to other sirens like MEZ, which wind-up relatively fast. Other fact known about the device, is that the DS977 is capable of running at 230V (single-phase electric power), which makes it a preferable civil defense siren for locations that have a limited or no access to three-phase power. However, this is at the cost of extending the wind-up time, due to lower voltage being delivered to the motor, therefore making the start-up slower. The siren can be recognized easily thanks to the start-up and its lower tone of 384 Hz. It has 8 ports. The DS977 usually came with two different types of covers. A vertically extended plastic cover, thanks to which it can be easily recognized (the device would be marked as DS977P) or an aluminium cover (DS977a).

The siren is a direct successor to S385. The counts of this version are not known.

In the Czech Republic, there are 5 052 sirens registered within the JSVV (Jednotý systém varování a vyrozumění - Unified warning and notification system), from which there are 4 621 sirens actively in use. (as of 17/6/2021)