Warning Broken Connection Charger

Detects whether the device is not connected properly to your offer
Suitable for battery chargers, portable supplies, etc.

Circuit diagram:

Parts:
R1______________10K, 1/4W
R2_______________1K, 1/4W
R3_______________1K, 1/4W Resistor (Optional Notes, see)

D1, D2________1N4007 1000V 1A Diodes
Red D3______________LED (optional Notes, see)

Q1, Q2_________BC557 45V 100mA PNP Transistors

BZ1___________Piezo probe (oscillator incorporating 3KHz)

Device Purpose:
The above circuit can be used to detect if the load of the battery charger or plug-in supply adapter is not connected properly. The load can be a set of batteries to charge, or any other type of battery or DC low voltage operation of the device.
The safety circuit can operate in a range of 3 to 15V and a maximum of 1A. current provided the voltage is about one volt higher than the voltage required by the load.

Circuit Operation:
The circuit is inserted between the supply and load, therefore, until a leak of the load current of at least 100μA is flowing toward the load, D1 and D2 performed. The voltage drop (about 1 V) available through the diode, Q2 units in the conduct and, consequently, Q1 is cut.
If there is no sensible load is connected to the output of the circuit will cut Q2, Q1 will conduct and the piezo-siren will beep.

Notes:
An optional LED and its series resistance limit can be connected in parallel to BZ1, as shown in dotted lines in the circuit diagram.
In this case you can omit the piezo tube to get a visual warning only.