Arduino project · Motion and security · Medium
Two-Layer Door Alarm (Reed + PIR)
The PIR gives a yellow warning for movement. If the door magnet is lifted the red LED and buzzer fire.
What you will learn
- How two sensors give two alarm levels
- How a warning is different from an alarm
- How a reed switch watches a door
How it works
Movement turns the yellow LED on as a warning. When the reed switch opens (magnet away) the red LED and buzzer come on as the real alarm.
Try this next
- Add a keypad to disarm the alarm.
- Add a delay for entry time.
- Send the alarm to your phone with a Bluetooth module.
The simulator program and explanation on this page are original. The idea follows a classic Arduino project that students have built for years.
Parts: sensors and actuators (tap to show or hide)
Try the inputs (virtual sensors)
Pins (you can change them)
| Part | Arduino pin (change it here) | How to wire it |
|---|
Every wire, one by one
Red rail = 5 V from the Arduino 5V pin. Black rail = GND. The coloured wires carry signals. Match the wire colours on the drawing to this list.
| # | Colour | From (part and leg) | To |
|---|
Steps run from top to bottom, then start again. While the simulation runs, the active step is highlighted in green.
Quantities come from the parts you added. The store links open a search for that item on Robu.in, Amazon.in and ThinkRobotics, so you always see what is in stock today. Check the model, voltage and price before you order.
| # | Item | Qty | Search term | Buy / compare |
|---|
The PDF has the circuit sketch, pin table, every wire, sequence, full code, the parts list with store links, do’s and don’ts for each part, and the safety notes. The project file lets you come back and keep editing.
In the real world
A two-layer burglar alarm
The door contact and the motion sensor both guard the room. Open the door or move in front of the sensor and the alarm sounds.
Tip: use the gold tab at the bottom of the circuit drawing to pull the real-world view up over the Arduino board. Your parts stay visible above it, so you can press a button and watch the real scene react.
- Reed switch = the door opens
- PIR sensor = a person moves inside
- Buzzer + LED = the alarm