Check Smart Doorbell Voltage and Identify Drop

What happens here

Finally, the electrician tests the voltage directly at the smart doorbell itself. Using the same multimeter, he connects the leads to the doorbell's terminals. The reading on the multimeter shows only 10 volts. This is significantly lower than the 18 volts measured at the transformer and the required voltage for many smart doorbells. This voltage drop is identified as the likely cause of the smart doorbell's intermittent operation, as it is not receiving sufficient power to operate consistently.

Goal: Determine the voltage supplied to the smart doorbell.