• Skip to main content
  • Skip to primary sidebar

Homemade Circuit Projects

Need circuit help? Post them in the comments! I've answered over 50,000!

Blog | Categories | About | Contact | Calculators-online
You are here: Home / Security and Alarm / Door Security Alarm Circuit for Alerting if Door was Opened

Door Security Alarm Circuit for Alerting if Door was Opened

Last Updated on August 25, 2023 by Swagatam 22 Comments

The door security alarm circuit discussed in this article alerts the user whenever the door fitted with the circuit is opened or closed or even moved from its original locked position.

Table of Contents
  • Using a Reed Relay and Magnet for the Triggering
  • Parts List
  • How it Works
  • Using IC 4093
  • How to Arm the Alarm

Using a Reed Relay and Magnet for the Triggering

The idea utilizes the very basic reed relay and magnet concept across the door and the door frame. The magnet is attached with the door edge, while the reed relay and its associated circuit is fixed on the door frame exactly adjacent to the door magnet, such that both are almost touching each other and separated only by the door and frame clearance.

Reed switch and magnet Installation on Door

This implies that whenever the door is moved or opened the magnetic influence on the reed relay is inhibited, which causes the associated circuitry to trigger the alarm.

The reed relay is connected with a delay OFF timer circuit, which makes sure that as soon as the door is opened or closed even for a fraction of a second causes the alarm to activate and sound for at least a few 10s of seconds, after which it automatically resets, until the door is moved yet again.

Magnetic Door Security Alarm Circuit

Parts List

  • Resistors 1/4 watt 5%
  • 10K = 1
  • 22K = 1
  • Capacitor Electrolytic
  • 1000uF/25V = 1
  • Transistors
  • BC557 = 1
  • 2N2222 = 1
  • Alarm = Any piezo alarm siren unit

How it Works

The arrangement can be seen in the above diagram which shows how the door open close alarm circuit needs to be configured which appears pretty straightforward.

As long as the door remains in the closed position, the magnet enables the reed in the switched ON or "closed" position, which in turn keeps the PNP BC557 switched OFF.

With BC557 switched OFF, the 2N2222 is also unable to conduct, and thus the connected alarm module continues to be silent.

However in a situation where the door is moved or opened by an intruder, causes the the magnet to shift from its original position, which instantly opens and releases the reed internal contacts.

The above action now enables the BC557 to conduct, subsequently enabling the 2N2222 also to trigger and ultimately switch ON the connected alarm unit.

The intruder realizes this and tries to close the door in an attempt to shut off the alarm, however due to the presence of the 1000uF capacitor, and the 22K resistor at the base of the 2N2222, the transistor continues to conducts ensuring that the alarm is not switched off even though the door is restored at its initial position....thus the alarm stays latched ON and continues to raise the alarm forcing the intruder to surrender himself, until the 1000uF capacitor has discharged completely.

This little inexpensive yet highly efficient door opening alarm circuit can be used for securing any desired entrance from a possible intrusion without the need of a constant monitoring or without a guard in position.

Using IC 4093

This door alarm circuit is constructed around an affordable CMOS 4093 integrated circuit (IC) and offers a battery-operated burglar alarm for doors. The system incorporates both entry and exit delay functionalities.

door security alarm circuit

The compact design of the unit makes it suitable to be enclosed in a small plastic enclosure, which can then be affixed to the inner side of the door requiring protection.

A small bar magnet is placed on the door frame, positioned within the range of the magnetic reed switch located in the alarm enclosure.

This setup ensures that the system functions as a self-contained unit, eliminating the need for any installation wiring.

How to Arm the Alarm

To activate the door alarm, simply turn the key switch from STANDBY to ON, and then leave the premises, ensuring the door is shut within 15 seconds (this time is determined by R2 and C1).

Subsequently, the alarm will arm itself, becoming responsive to any door openings. A flip-flop circuit constructed around IC1 b and e is utilized here.

Upon activation, C2 starts to charge through R4, creating an entry delay period lasting 20 seconds.

If the system is not switched back to the standby mode, the voltage across C2 eventually reaches the threshold of IC1 d.

As a result, Q1 energizes the piezo buzzer, triggering the audible alarm.

Resetting the system to its original state can be accomplished at any time by reverting the key switch to the STANDBY Mode.

The power consumption of the unit in both its active and standby states, without triggering the alarm, is minimal, enabling extended operation over time using a 9V PP3 battery.

You'll also like:

  • 1.  PIR Burglar Alarm Circuit
  • 2.  3 Accurate Infrared Intruder Alarm Circuits using Photodiodes
  • 3.  Power Interruption Alarm Circuit for Instant Power Failure Indications
  • 4.  SMS Based Laser Security Circuit
  • 5.  Make this Simple Refrigerator Door Open Alarm Circuit
  • 6.  Loop-Alarm Circuits – Closed-Loop, Parallel-Loop, Series/Parallel-Loop

About Swagatam

I am an electronics engineer with over 15 years of hands-on experience. I am passionate about inventing, designing electronic circuits and PCBs, and helping hobbyists bring their projects to life. That is why I founded homemade-circuits.com, a website where I share innovative circuit ideas and tutorials. Have a circuit related question? Leave a comment.... I guarantee a reply!

Previous Post: « Arduino based DC Voltmeter Circuit – Construction Details and Testing
Next Post: LPG Leakage SMS Alert using MQ-135 – Get Warning Message in your Cellphone »

Reader Interactions

Comments

  1. IOANNIS PIPPAS says

    May 14, 2025 at 1:18 am

    ΟΚ THANK YOU I WILL TRY IT WITH A VIBRATION SPRING

    Reply
  2. IOANNIS PIPPAS says

    May 13, 2025 at 1:19 am

    Hello,
    I’m looking for a simple vibration alarm circuit. The one I can’t find is the one that, when activated, sounds for a certain amount of time, which I can adjust to set how long it will sound.
    Not a circuit that delays activation, but one that sounds for a configurable period once triggered.

    Reply
    • Swagatam says

      May 13, 2025 at 7:48 am

      Hello, you can try the first circuit from the following article. You can adjust the C2 value to change the delay OFF timing of the relay:
      https://www.homemade-circuits.com/simplest-sound-activated-relay-switch/

      Reply
  3. Brian says

    December 20, 2022 at 11:54 am

    Hi there great little circuit. Instead of using the reed relay this could be hooked up to either the dome light or door open lamp indicator on the dash as an effective car alarm. Am I correct in saying that. Also using a higher rated capacitor would that keep the alarm sounding longer until discharged.
    I could be wrong and I apologise for my lack of knowledge but are learning. Just wanting to build a simple but effective vehicle alarm.

    Reply
    • Swagatam says

      December 20, 2022 at 1:23 pm

      Hi, you are absolutely right with your assumptions. That would certainly work.
      You can tweak the 1000uF capacitor or the 22K resistor or both to optimize the output time delay, as desired.

      Reply
  4. jim Wiggs says

    March 7, 2020 at 8:19 am

    I read your artical on magnetic switch alarm What im doing is setting up a 12 volt door alarm and need to know what timer I need. I want the alarm to remain on for a set time after switch is tripped even if door is closed and switch is reset I need the alarm to continue for preset time. Would a simple time delay switch work?

    Reply
    • Swagatam says

      March 7, 2020 at 9:13 am

      The mentioned feature is already included in the design. The 1000uF capacitor ensures that the alarm runs for some time even after the door is closed

      Reply
  5. Revanth says

    November 2, 2019 at 2:29 am

    What is the use of transistor and why it generates low frequency
    Pls solve my query

    Reply
    • Swagatam says

      November 2, 2019 at 11:56 am

      transistors are not generating any frequency, the alarm is supposed to have built inbuilt oscillator.

      Reply
  6. David Birchall says

    December 14, 2017 at 11:39 pm

    Hello Sir,

    On Door Security Alarm Circuit.

    1. How would I calculate the size of Resistor and Capacitor to give an approximate ON time of 10 minutes once the alarm has been activated

    2. What is the maximum safe current the transistors BC557 and 2N2222 can carry

    Any advice will be welcomed

    Reply
    • Swagatam says

      December 15, 2017 at 7:35 am

      Hello David,

      I am sorry I do not have the formula for RC network, you will have to find the right value through practical testing. By the way 10 minutes is not feasible in the above design unless you add another transistor in it…

      Reply
    • Swagatam says

      December 15, 2017 at 7:36 am

      BC557 can handle 100ma, 2N2222 1Amp on heatsink

      Reply
  7. Jonathan Forson says

    May 22, 2017 at 1:12 pm

    hi sir, can u please help me out with a breadboard version of the door alarm circuit

    Reply
    • Swagatam says

      May 22, 2017 at 2:28 pm

      Hi, Jonathan, breadboard is not recommended for such a basic and a small design, you must use a strip board and solder the parts instead…

      Reply
  8. Sharoj Al Hasan says

    October 10, 2016 at 7:18 am

    Sir please help me I want a timer circuit it will Turn the relay on 15 second And Turn the relay OFF 15 Seconds Continiusly

    Reply
  9. debasisneogi says

    October 4, 2016 at 5:51 pm

    Sir would you please discuss remote controlled calling bell next,? If you do it will be very helpful. Regards.

    Reply
    • Swagatam says

      October 5, 2016 at 6:04 am

      Debasis, I already have it in my website you can search it through the search box…

      Reply
  10. Chisom Kester says

    October 3, 2016 at 9:57 pm

    Thank you sir for this circuit

    Reply
    • Swagatam says

      October 4, 2016 at 1:33 am

      you are welcome Chisom

      Reply
    • Unknown says

      October 23, 2016 at 2:01 pm

      Sir… Can u please help me out with a project proposal on DOOR OPEN CLOSE ALARM CIRCUIT.

      Reply
  11. Tun says

    October 2, 2016 at 2:51 pm

    Hi sir, i wanted to ask you if it is possible to build an homemade flashdrive( i.e any storage device) or not. And pls i need your help.

    Reply
    • Swagatam says

      October 3, 2016 at 3:55 am

      Hi Tun, according to me it's not possible…

      Reply

Need Help? Please Leave a Comment! We value your input—Kindly keep it relevant to the above topic! Cancel reply

Your email address will not be published. Required fields are marked *

Primary Sidebar

Subscribe to New Circuit Ideas

Categories

  • Arduino Projects (87)
  • Audio and Amplifier Projects (132)
  • Automation Projects (17)
  • Automobile Electronics (101)
  • Battery Charger Circuits (83)
  • Datasheets and Components (104)
  • Electronics Theory (143)
  • Free Energy (37)
  • Games and Sports Projects (11)
  • Grid and 3-Phase (19)
  • Health related Projects (25)
  • Home Electrical Circuits (12)
  • Indicator Circuits (14)
  • Inverter Circuits (87)
  • Lamps and Lights (142)
  • Meters and Testers (69)
  • Mini Projects (46)
  • Motor Controller (64)
  • Oscillator Circuits (27)
  • Pets and Pests (15)
  • Power Supply Circuits (108)
  • Remote Control Circuits (50)
  • Security and Alarm (64)
  • Sensors and Detectors (101)
  • Solar Controller Circuits (59)
  • Temperature Controllers (42)
  • Timer and Delay Relay (49)
  • Transmitter Circuits (29)
  • Voltage Control and Protection (37)
  • Water Controller (36)

Calculators

  • Battery Back up Time Calculator
  • Capacitance Reactance Calculator
  • IC 555 Astable Calculator
  • IC 555 Monostable Calculator
  • Inductance Calculator
  • LC Resonance Calculator
  • LM317, LM338, LM396 Calculator
  • Ohm’s Law Calculator
  • Phase Angle Phase Shift Calculator
  • Power Factor (PF) Calculator
  • Reactance Calculator
  • Transistor Astable Calculator
  • Transistor base Resistor Calculator
  • Voltage Divider Calculator
  • Wire Current Calculator
  • Zener Diode Calculator
  • Filter Capacitor Calculator
  • Buck Converter Calculator
  • Boost Converter Calculator
  • Solar Panel, Inverter, Battery Calculator
  • Wire Current Calculator
  • SMPS Transformer Calculator
  • IC SG3525, SG3524 Calculator
  • Inverter LC Filter Calculator

People Also Search

555 Circuits | 741 Circuits | LM324 Circuits | LM338 Circuits | 4017 Circuits | Ultrasonic Projects | SMPS Projects | Christmas Projects | MOSFETs | Radio Circuits | Laser Circuits | PIR Projects |

Recent Comments

  • Swagatam on EGS002 Datasheet, Circuit Diagram Explained
  • Swagatam on How to Make IC LM339 Circuits
  • Swagatam on How to Make Dog Barking Preventer Circuit using High Frequency Deterrence
  • Swagatam on How to Buy and Use RF Remote Control Modules – Control Any Electrical Gadget Remotely
  • Swagatam on How to Generate PWM Using IC 555 (2 Methods Explored)

Company

  • Privacy Policy
  • Cookie Policy
  • About Me
  • Contact
  • Disclaimer
  • Copyright
  • Videos
  • Sitemap

Social Profiles

  • Twitter
  • YouTube
  • Instagram
  • Pinterest
  • My Facebook-Page
  • Quora
  • Stack Exchange
  • Linkedin
  • © 2025 · Swagatam Innovations