What does ha stand for in the circuit?

HA stands for sound indicator in the circuit.

1. Circuit: A conductive loop consisting of metal wires and electrical and electronic components is called a circuit. When a power supply is added to the input of the circuit, a potential difference is generated at the input, and the circuit can work.

2. Some phenomena can be seen intuitively, such as the deflection of voltmeter or ammeter, light bulb lighting, etc. Some people may need measuring instruments to know whether they are working properly. According to the nature of current flow, it is generally divided into two types. The circuit through which direct current passes is called "DC circuit" and the circuit through which alternating current passes is called "AC circuit".