Here's why:

* Safety: Doorbells are wired to your home's electrical system. Working on live wires can result in electric shock, potentially causing serious injury or even death.

* Preventing damage: Turning off the power ensures you won't accidentally damage the doorbell or the wiring while working on it.

Here's how to safely change a doorbell:

1. Locate the circuit breaker: Find the breaker that controls the doorbell. This is usually on your electrical panel.

2. Turn off the power: Flip the breaker switch to the "off" position.

3. Test the circuit: Use a non-contact voltage tester to confirm that the power is off.

4. Change the doorbell: Proceed with the replacement as per the instructions.

5. Turn the power back on: After you have successfully installed the new doorbell, turn the power back on and test the new doorbell to ensure it works properly.

Always prioritize safety. If you are not comfortable working with electricity, it's best to call a qualified electrician.