Refrigerator Alarm: What Is It and How It Works?

Have you ever discovered your fridge door was slightly open all along and most of your food has gone wrong? Or, does your fridge door need that extra push to close properly? Well, you’re in luck because we have a solution for you. What you need is a refrigerator alarm with a control panel.

An audible refrigerator alarm is easy to make and set up. Plus, it’s a less expensive solution for your refrigerator door problems.

So, in this article, we will show everything you need to know about refrigerator alarms and how to make an easy fridge alarm circuit.

What is a Refrigerator Alarm?

The refrigerator door alarm circuit triggers an alarm if you leave your refrigerator door open for some time. 

Here’s what happens when you leave the door of your fridge open. First, the fridge cabin will become hotter than usual. 

Next, the thermostat will sense this increase in temperature and try to cool down the cabin. Thermostats always try to maintain the working temperature of a refrigerating system. But, if your refrigerator has a display panel, you can see the indicators via alarm icon flashes or alarm sensors.

Open Refrigerator

Open Refrigerator

Also, the compressor will work continuously to dissolve the heat entering the cabin. Thus, increasing the power consumption from the receptacle. 

What’s important here is that if the refrigerator continues to work under this condition, it would reduce the compressor’s lifespan and cause it to malfunction. 

For this reason, the fridge door alarm is what you need—if you have this problem.

How Do Refrigerator Alarms Work?

A refrigerator alarm functions as a reminder to know when the fridge door is open by sending signals. The sensor is responsible for detecting when to sound the alarm signal. 

The sensor of the refrigerator alarm sound is an LDR. So, when light from the refrigerator or an external bulb falls on the LDR sensor, it reduces its resistance. After some time (about 10 seconds), the capacitor voltage reaches the threshold of the circuit. 

For this reason, the circuit generates a square wave signal with several Hertz frequencies and sends it to the tone oscillator. The amplifier amplifies the tone signal and drives the ceramic transducer—which doubles the frequency.

Additionally, you can easily adjust the LDR’s light sensitivity and the alarm tone to match the resonant frequency of the ceramic transducer.

Plus, you can get the maximum volume level when the tone frequency is equal to the resonant frequency of the ceramic transducer.

The audio alarm or beeps will turn off when no light is hitting the LDR.

DIY Refrigerator Door Alarm

Now, let’s look at building a simple DIY refrigerator alarm using a 555 timer IC. Here’s the circuit we’ll be working with:

Circuit Description

When you shut the fridge door, the LDR’s resistance is almost 1MΩ. Now, the potential divider’s output voltage shows across the capacitor, but it stays in charged condition. Thus, producing a low output. However, when you leave the fridge door open, light falls on the LDR and lowers its resistance, allowing the capacitor to discharge. For this reason, the output begins oscillating to a specific frequency. Hence, the work becomes HIGH. 

Furthermore, the capacitor charges again and reaches a threshold set by the discharge of the capacitor. This process keeps going until the resistance of the LDR becomes high again—which happens when it doesn’t detect light.

While this happens, the second timer IC begins oscillating and switches its output between high and low. Plus, it allows the LED and buzzer connected to the timer IC to blink and beep in a fluctuating pattern. 

These patterns are combinational due to the inner oscillation of the second timer and the change of the first 555 timer.

When the first timer’s output becomes HIGH, the second timer’s RESET will trigger. Thus, allowing the capacitor (C2) to charge and produce a low result. But, in a short period, the capacitor will discharge and make the output HIGH. Thus, the buzzer linked to the output will generate a beeping sound.

Circuit Components

Here are the components you need to build this circuit:

  • 555 timer IC (2)
  • 5mm LDR (1)
  • Small Buzzer (1)
  • 5mm LED (1)
  • 1n4007 Diode (1)
  • 47uf Electrolytic Capacitor (1)
  • 0.1uf Ceramic Capacitor (1)
  • Resistors – 10K’Ω – 1; 470K’Ω – 2; 100K’Ω – 1; 100’Ω (4)
  • PCB (1)
  • Connecting wires
  • 9V battery (1) 


Using a PCB from time to time for this circuit makes it even easier. All you have to do is follow these steps, like a user manual, and place the components according to the printed circuit board. Here are the steps:

Step 1- Gather Components

Before building anything, always make sure you have all the necessary details and tools. Check the above list to know the essential components and classic products required to build the circuit.

Step 2- Solder Your Base

Solder the base of your timer ICs before placing them on your PCB.

Step 3 – Circuit Assembly

Once you solder the base of your timer ICs, the next step is to place them on the PCB. Next, get your resistors and solder them to the PCB as well. (Ensure you follow the markings on the PCB).

Step 4 – Circuit Assembly 2

Now, solder your capacitors (ceramic and electrolytic), diodes, LED, LDR, buzzer, and finally, the power connector.

Multicolored LEDs

Multicolored LEDs





Step 5 – Final Test

Last but not least, power up your circuit by connecting it to the 9V battery, test it to check if everything works fine, and make the necessary alarm adjustments.

Advantages of a Refrigerator Door Alarm

Here are some advantages of having a refrigerator door alarm in your home:

  • Fridge door alarms are easy to produce
  • You can customize and set the alarm key 
  • It can save you from food loss
  • It’s not expensive
  • It’s also easy to install and maintain
  • Can save you a lot of electricity costs and spend less for your power supply

Final Words

The refrigerator door alarm is one of the easiest projects out there for engineers, DIYers, and designers. Plus, it’s helpful and prevents you from shortening the lifespan of your refrigerator.

It’s also a great way to know when kids or animals are sneaking a treat at night. However, there are other ways to make a fridge alarm, like the regular circuit without the timer IC and the door entry alarm hack. We feel the timer IC circuits give the best result for an alarm-type course.

Well, that wraps up this article. If you have any questions or suggestions, feel free to contact us, and we’ll be happy to help.

Avatar photo
Emma Lu
Our professional engineering support saves our customers a lot of trouble and loss. >>>>>> After you place the order, our engineer will conduct technical reviews to make sure the parts can be mounted well/correctly on the boards. We will check if the component packages match well with the Gerber footprints, if the part numbers you provided match well with the descriptions, and if the polarity is clearly marked. >>>>> When your design is ready, please send your Gerber and BOM so we can quote and start!