Invisible Touch Alarm System for Doors

In this project, I’ll show you how to build a simple but effective door alarm system using a TTP223 touch sensor, IRFZ44N MOSFET, and a buzzer — all powered by a single 18650 battery.

This alarm system is designed to trigger instantly when someone touches your door handle, even while wearing gloves, thanks to the capacitive sensing feature of the TTP223. When activated, a loud buzzer sounds to alert you of any suspicious activity or attempted entry.

To stop the alarm, simply press a reset push-button, which instantly turns the system off and re-arms it for the next touch.

It’s a great DIY project for basic home security, easy to build, requires very few components, and mounts neatly on any door using acrylic and copper wire.

Let’s get started!

1. TTP223 Touch Sensor – 1
2. IRFZ44N MOSFET – 1
3. PC817 Optocoupler – 1
4. Push-On Switch (Reset Button) – 1
5. Buzzer (3V–5V) – 1
6. 18650 Battery Holder – 1
7. 18650 Li-ion Battery – 1
8. 220 Ohm Resistors – 2
9. Connecting Wires – as needed

1. Identify the 3 pins on the TTP223: OUT (1st), VCC (2nd), and GND (3rd)
2. Gently bend the 1st pin (OUT) and 3rd pin (GND) outward for easy connection
3. Keep the 2nd pin (VCC) straight for connecting to battery positive
4. Cut the extra length of the bent pins using a wire cutter
5. Connect the 3rd pin (GND) of TTP223 directly to the Source pin of the IRFZ44N MOSFET
6. Ensure no pins are touching each other after bending

1. Take the push-on switch (2 legs)
2. Solder one leg of the switch to the 1st pin (Gate) of the IRFZ44N MOSFET
3. Take a 220Ω resistor
4. Solder one side of the resistor to the same 1st pin (Gate) of the IRFZ44N

1. Cut the excess legs of the PC817 optocoupler to keep the layout compact
2. Connect the 1st leg (anode) of PC817 to the free side of the 220Ω resistor (the same resistor connected to IRFZ44N Gate)
3. Connect the 2nd leg (cathode) of PC817 to the VCC pin of the TTP223 touch sensor

1. Take another 220Ω resistor
2. Solder one end of the resistor to the 1st pin (VCC) of the TTP223 touch sensor
3. Solder the other end of the resistor to the 4th pin of the PC817 optocoupler

1. Take a 3mm acrylic sheet — this will be the base for your circuit
2. Place all components neatly and glue them onto the acrylic sheet
3. Use thick copper wire to make strong solder bridges between components
4. Solder the 1st leg (Gate) of the IRFZ44N MOSFET to the 3rd pin of the PC817 optocoupler

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1. Take another piece of thick copper wire
2. Connect it from the GND line of the circuit to the GND terminal of the 18650 battery holder
3. Glue the 18650 battery holder onto the acrylic sheet securely
4. Solder the VCC pin (1st leg) of the TTP223 to the positive terminal of the 18650 holder

1. Take a 3V to 12V DC buzzer
2. Glue it onto any free space on the acrylic sheet
3. Solder the negative (–) leg of the buzzer to the center pin (Drain) of the IRFZ44N MOSFET
4. Solder the positive (+) leg of the buzzer to the VCC pin (1st pin) of the TTP223 touch sensor

1. Gently scratch the copper pad area of the TTP223 sensor to expose clean metal
2. Solder a single wire to this pad — this will act as the external touch contact (can be attached to a door handle or metal plate)
3. After confirming all wiring is done, take 4 pieces of acrylic sheet to cover all sides of the project
4. Glue all edges securely to fully enclose and protect the circuit
5. Optionally, seal all open points with a small amount of hot glue for durability and insulation

1. Insert a fully charged 18650 battery into the battery holder
2. Once powered, your circuit is active and ready to use
3. Touch the wire connected to the TTP223 sensor — the buzzer should turn ON immediately
4. Now press the push-button switch — this will reset the system and turn OFF the buzzer

1. Fix the completed acrylic unit near the door handle, using screws or strong double-sided tape
2. Take the touch wire (connected to the TTP223 sensor) and attach it securely to the metal handle or handle frame
3. Make sure the exposed wire touches or wraps around part of the handle where a person would normally place their hand
4. This setup allows the system to detect touch even through gloves, thanks to the capacitive sensing of the TTP223
5. When someone touches any part of the handle, the buzzer activates immediately
6. To turn off/reset the alarm, simply press the push-button switch

1. Once everything is mounted and powered, the system is fully armed
2. If a thief touches the door handle, even while wearing gloves, the TTP223 detects the touch
3. The alarm buzzer sounds immediately, drawing attention and alerting everyone nearby
4. As the theft runs away, the system stays active until someone presses the reset button to turn off the buzzer

✅ Your DIY Touch-Activated Door Alarm System is now fully complete and working as intended!

📽️ Watch the full video demo here:

👉 CLICK HERE