Replace the panel cover and turn the circuit on that controls the smoke detectors. CAUTION! Look away when turning on the breaker and step to one side of the panel. Never stand directly in front of a panel when turning on and off breakers.
Go to the smoke detector and push the test button. You’ll need to hold the button in for a few seconds until it sounds an alarm. Be sure to have someone walk around to all of the other detectors to check if they are also going off. With the interconnection wire, they should all be sounding.
Release the button and it should go silent again. That’s all there is to installing smoke detectors.