How Do Contact Sensors Work | Things I Wish I’d Known Earlier


Articles, products, and services offered on this site are for informational purposes only. We are part of the Amazon Services LLC Associates Program, an affiliate advertising program. is compensated for sales resulting from links on our website.

Please review our disclaimer before acting based on anything you read or see.

Many people ask how do contact sensors work. Contact sensors, also known as limit switches, are electrical, pneumatic, or mechanical devices that are located at the end of the path of an object or moving element such as a conveyor belt or the arm of a robot, for example. They have an obvious purpose, which is to convert a physical quantity into an electrical one, that is, to allow through contact (physical quantity) to give the signal (electrical quantity) that an object has already reached its final disposal. Furthermore, contact sensors are an essential part of security systems and smart homes. Although initially designed to detect when an intruder opens a window or door, the device has evolved over the years to provide more functions.

It provides the data needed for smart homes to take intelligent actions. Contact sensors can turn on lights, trigger smart door alarms or control smart thermostats and other functions on a Smartphone. Many homeowners tend to ask “How do contact sensors work”. This question has been adequately answered in the preceding sections below.

How do Contact Sensors Work

The contact sensor tells the security system, whether doors and windows are closed or open. They can be installed on windows, doors and even desk drawers throughout the house. The contact sensor is divided into two parts, one part is installed on the window or door, and the other part is fixed on the window or door frame. During installation, the two sensors are placed next to each other. Built to use magnetic fields, these two parts track the movement of the door. If the door is opened, they will separate, causing the contact sensor to transmit an “open” signal to the security system.

Types of Contact Sensors

Contact sensors can be classified by their structure and operation, in the same way, they can be grouped depending on the area of application in conventional and industrial fields. Currently, there are two types of contact sensors according to the way they work and their structure. These are:

Binary Contact Sensors

Binary contact sensors, as their name indicates, respond to two operating states under the presence or absence of an object, which translates into binary logic like all or nothing, hence its name.

Since binary sensors are contact devices that respond to the presence or absence of a specific object, they have two contact positions ordinarily open (NO) and normally closed (NC). Examples of these devices are micro-switches, limit switches and push buttons; each one has specific characteristics and uses.  

These sensors have two types of positive and negative operation:

Positive: In this mode, the sensor is activated when the element to be controlled makes the axis rise and connects to the moving object with the NC contact. When the spring (pressure spring) breaks, the sensor remains disconnected.

Negative: In negative mode, the opposite happens, when the controlled object has a protrusion that pushes the shaft downwards, forcing the cup spring and causing the circuit to close. In this mode, the spring fails and breaks while remaining activated.

Analog Contact Sensors

On the contrary, analogue sensors not only detect the presence of a specific object; they also provide an output signal proportional to the force exerted. Therefore, an analogue contact sensor is a handy device whose output is proportional to a local force. The simplest of these devices is constituted by a spring-actuated rod that is mechanically linked to a rotating axis, in such a way that the displacement of the rod due to a lateral force gives rise to a proportional rotation of the axis.

At present, different analogue contact sensors can vary in characteristics depending on the area for which they are manufactured so that we can find various analogue sensors aimed for the area of home security.

Parts of a Contact Sensor

In a contact sensor, we can distinguish several parts, which are common to all of them regardless of the type, below we detail each of the parts with its characteristics:

Actuator: This element is the one that directly contacts the mobile object. It has two positions, rest and operation.

Head: This is where the mechanism that transforms the movement of the actuator into the contact movement of the stroke sensor is located. Thus, when the actuator moves correctly, the head mechanism actuates the switch contacts.

Contact block: This is where all the electrical part of the switch contact is located.

Terminal block: It is in this area where cables connect the switch with the rest of the control circuit.

Switch body: Depending on the type of switch, inside, we will find some elements or others. In a plug-in switch, we will find the contact block while a non-plug-in switch will have the contact block and terminals.

Base: Non-plug-in switches do not have one, while in plug-in switches the base houses the terminal block.

How do Contact Sensors Work: Their Merits for the Home

Because they can determine the presence, absence, passage and position of an object, their use is widespread in the field of home security. This includes:

Doors and Windows

Contact sensors are composed of sensors and magnets. When they are connected to a window or door, they will alert the homeowner when they are opened. The combined door/window contact sensor has areas that are easy to bypass without the need to manually arm and disarm the system until the next contact closure.

The size of the mini door/window sensor is about 2 inches and can be placed on almost all doors. The remote wireless function can increase power and battery life, which can also provide long-lasting protection. You can also consider using a stylish wireless NanoMax Mini transmitter for easy internal compatibility.

How Do Contact Sensors Work

Garage and Gate 

With the support of encryption technology, encrypted thin door/window contact sensors can resist potential intruders and system hackers. This model is most suitable for garage doors, backyard and pool security doors, and other open/close objects. Its tamper-proof cover prevents harsh environments, vandalism and theft.

Drawers, Cabinets and Appliances 

For health benefits, touch sensors can be added to kitchen and bathroom cabinets, drawers and common household appliances. They can also help confirm that your loved one is taking medication and maintaining healthy eating habits, for example, by signaling a half-open refrigerator/freezer door.

what is contact sensor

Glass Break Sensors

Sometimes called glass detectors, they notify the homeowner if glass windows and doors break. Unlike window sensors, glass break sensors are activated by noise or vibration of broken glass.

how do automatic door sensors work

How Do Contact Sensors Work: Frequently Asked Questions

How close do ring contact sensors need to be?

With regards to ring contact sensors, their closeness needs to be at least 1 inch or less.

How do you test a ring contact sensor?

To test a ring contact sensor, do make use of the following steps:

  • Open your Ring app
  • Click the menu
  • Click on the device
  • Now, click “Alarm Base Station”
  • Click on the ring contact sensor you want to test
  • Click Test exercise
  • Please move to the front of the ring contact sensor you want to test and make sure it works properly

Are window sensors useful?

Yes. Window sensors are a unique and beneficial addition to any home security system. They are cost-effective and can deter thieves before causing further harm. If you don’t have these tools yet, please consider buying one, as window sensors may be the last part of your home security system you need.

Does every room need a glass break sensor?

One glass break sensor per medium-sized room usually solves the problem. Generally, the glass break sensor can protect three windows.

How long do glass break sensors last?

The wireless glass break sensor design to work for at least one year. After this time, you can then replace the battery according to the purpose.


In conclusion, contact sensors are electrical, pneumatic or mechanical devices located at the end of the path of a mobile element or on the mobile itself, for example, a conveyor belt or security windows. The most used in educational projects are also the limit switches for the design of some simple projects. Example: positioning of a moving object concerning a fixed one, returning it to the correct direction.

Regardless of the purpose for which a contact sensor manufacture, its function is to convert a physical quantity into an electrical quantity. And in this way detect and initiate a specific operation within an electrical or electronic circuit.

Furthermore, contact sensors are the simplest and most basic. And they activate the moment they come into contact with an object. And as previously highlight above, contact sensors use to detect the end of travel or the limited position of mechanical components. For example: To find out if a window or door is fully open or close, or to activate the direction change of a motor or to stop it. In all, learning how to contact sensors work is paramount for your home’s security as highlighted above.

Read More: How Many Types of Vibration Sensors

Comments are closed.