This circuit is from the 1983 Intersil Databook. The display is plasma and must be excited by a high voltage circuit. The components used in this configuration are not common today.
In fact, this is the circuit also known as “vox”, that is, a relay triggered by sound. This...
Based on an LM36000 OTA this circuit was found in the July 1988 issue of Radio Electronics...
Relays up to 100 mA can be driven by the 555 with the recommended circuit. The circuit is from an...