How to Build a Door Alarm with Alarm Lamp and Door Sensor

Place the sensor and lamp

Mount a Door sensor on the block next to your door frame so it faces the door. Place an Alarm Lamp on a wall or ceiling where you can see it from inside. Run redstone dust from the Door sensor output to the Alarm Lamp input.

Wire and test

When the door opens, the Door sensor emits a redstone signal that lights the Alarm Lamp. If you want a sound as well, place an Alarm Siren next to the Alarm Lamp and connect it to the same redstone line. Both blocks accept a standard redstone signal, so a single dust line powers them together.

To silence the alarm without breaking the circuit, insert an Industrial Lever or a Glass Button between the sensor and the lamp. Flipping the lever cuts power to the lamp and siren while leaving the sensor wired for later use. For a touch-free variant, swap the Door sensor for an Industrial Door Contact Mat placed on the floor in front of the door; stepping on the mat triggers the same Alarm Lamp and Alarm Siren.

Test by opening the door. If nothing lights, check that the Door sensor is oriented toward the door and that the dust line reaches the Alarm Lamp's input face.