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how does freestyle libre work

How does Freestyle Libre work

*Disclaimer: All content and information in this blog is for informational and educational purposes only.
This article was written by Pete Lomas (T1D) and medically reviewed by Rachael Baker, BNg, CDE, MNgPrac
Last updated on 08/02/24.


I’ve been wearing a Freestyle Libre for over 5 years now and I can say unequivocally that this technology is a game changer and a fascinating piece of kit that actually makes you healthier and more in tune with your metabolism and blood sugars.

How does the Freestyle Libre sensor attach? 

In short…it’s pretty easy.  In the Libre kit you get:

  • A sensor pack (contains the actual glucose sensor that sticks to your skin)
  • A sensor applicator (applies the sensor to your skin)
  • An alcohol wipe – prepares the skin pre-application

The Freestyle Libre parts are the sensor and the reader. The sensor is the small, round device that includes a tiny, flexible wire inserted just under the skin to measure glucose levels continuously. The other component, the reader, is a handheld device that scans the sensor to display real-time glucose readings, historical data, and trends.

how does freestyle libre work

The sensor pack and applicator attach to each other and this inserts the sensor into the applicator ready for attachment to your body.  I recommend setting the sensor pack on a flat surface and pushing the applicator down into the sensor pack.  This minimizes risk of attachment issues.

Then clean the skin, place the applicator in the area you want to apply to and press down.  This injects the sensor into your arm.  I hold it for a few seconds to ensure adhesion.

Tip: I apply a new sensor 60 minutes prior to the old sensor running out and use my Libre scanner to start the new sensor and keep the old sensor linked to my iPhone app.  This helps me avoid the one hour lag and calibration time so I have no gap in my readings. I apply the new sensor right next to the old one on the same arm.

Read more about Why Freestyle Libre CGM is a game changer for T1D

Learn also How to build your own CGM with Libre and Miao Miao

FreeStyle Libre Sensor Placement

The recommended location to apply is the back of either arm.  Although you will find that many Libre users apply in other locations dependent upon their needs and preferences.  I have always used the back of my left triceps (see video below). While the upper arm is a common site for the FreeStyle Libre sensor, individuals may choose Freestyle Libre alternative sites for reasons such as comfort, precision, or personal preference.

Diabetics often find it hard to install their sensors on the parts of the body already covered with a tattoo. Placing a Libre sensor on a tattooed area of the body can lead to several issues. The sensor may not adhere properly and can come loose during intense physical activities. You might encounter difficulties ensuring it stays securely in place.

Abbott, the FreeStyle Libre CGM product line manufacturer, generally recommends that users avoid applying the sensors on skin regions with moles, scarring, and tattoos. This is because these skin regions can reduce the firmness of the sensor on the skin, causing it to slip off more frequently. In some reported cases, diabetics have found that the extra layer of ink in the skin reduces the firmness of the sensor, resulting in it slipping off more frequently.

Speaking about activities like swimming, running or jogging, there’s a risk the sensor could detach. A sensor that doesn’t fit snugly can ruin your activity, your blood glucose management, and your day. It’s essential for the sensor to remain tightly affixed to the skin to provide continuous and accurate blood glucose monitoring. Sensors that frequently dislodge disrupt the continuity of glucose level tracking, leading to gaps in daily monitoring. Because many people asked, we provided some very useful tips for swimming with a Freestyle Libre sensor.


Does Freestyle Libre have a needle? 

Many T1D patients often wonder whether the Freestyle Libre have a needle. I want to clarify that the Freestyle Libre uses a tiny, flexible sensor wire, not a traditional needle. The sensor needle houses the sterile filament that is inserted in the skin.  The needle is the delivery mechanism for the filament. The Freestyle Libre sensor is inserted just under the skin’s surface, into the subcutaneous tissue, by a small skin puncture, usually on the back of the upper arm, with a simple applicator. It gets the sterile filament into the skin and then the needle comes out, leaving the filament left behind.  It may look scary but in truth 95% of the time there is no pain.

The process is quick and relatively painless, and once inserted, the sensor continuously measures glucose levels in the interstitial fluid. It’s a great alternative to traditional fingerstick testing, offering a convenient and comfortable way to monitor blood sugar levels without the need for frequent needle pricks.


Does Freestyle Libre hurt? Is it painful?


“Does Freestyle Libre hurt?” This is a common question among individuals considering the Freestyle Libre system. Rest assured, the process is generally well-tolerated. To reiterate…there is rarely any pain.  On random occasions there’s a sting and even a little blood.  But I can’t remember the last time I had pain or blood. The sensor is designed to be small and unobtrusive and while you may feel a brief sensation during insertion, most users report minimal discomfort. The beauty of the Freestyle Libre system lies in its ability to provide continuous glucose monitoring without the need for frequent, painful fingerstick tests. The brief discomfort during sensor application is outweighed by the convenience and benefits of continuous glucose monitoring.


How does it read your sugar level?


This is the fun part.  The filament contains an enzyme called glucose oxidase, this enzyme reacts with the interstitial fluid, converts glucose to hydrogen peroxide.  A current is then generated which is electronically transmitted to your reader or smartphone app.

For a more detailed scientific understanding on how does the sensor measure glucose here’s one of many articles that digs deeper.

It’s important to note that this is an interstitial reading not a blood reading.  It is a proxy for a blood reading.  It’s good enough for me.

Diagram courtesy Abbott


Freestyle Libre sensors available on the market in 2024

There are three types of FreeStyle Libre continuous glucose monitoring (CGM) systems currently on the market in 2024:

  1. FreeStyle Libre: The original version, introduced by Abbott Diabetes Care and FDA approved in 2017, is known for its “flash glucose monitoring” capability. It features a disposable 14-day sensor probe that is placed under the skin and is factory-calibrated, thus not requiring calibration against a fingerstick glucose test​​. To read your glucose numbers, you wave the monitor in front of the sensor. It is advisable to carry out the procedure multiple times daily. Alternatively, you can use a smartphone app designed for the Freestyle Libre for scanning, instead of relying on the monitor.Unlike the original Libre system, which lacks alerts for low or high blood sugar levels, the Libre 2 system is equipped with such alarm features. 
  2. FreeStyle Libre 2: An advanced version of the original FreeStyle Libre, which includes additional features such as optional real-time glucose alarms that notify users when their glucose levels are too high or too low​​. Although the Libre is designed for adult use, the Libre 2 is appropriate for children.

Learn more about Freestyle Libre 2.

3. FreeStyle Libre 3: The latest version, which offers the smallest and thinnest CGM sensor from Abbott, providing real-time glucose readings directly to a smartphone or device without the need for a separate reader. It’s designed to be even more discreet and convenient for users, with enhanced accuracy and performance​​.

Learn more about Freestyle Libre 3. and The differences between Libre 3 and Libre 2.

Each version of the FreeStyle Libre system offers unique features tailored to different needs and preferences, making it easier for people with diabetes to manage their glucose levels effectively.


How much does the Libre CGM costs

May vary from country to country but in general terms you’re looking at $75 USD to $80 USD per sensor and a sensor lasts 14 days.  Assuming you protect it with one of our patches for freestyle libre sensor.


How to cover Freestyle Libre sensor (with patches)


This is most definitely in our wheelhouse here at Not Just a Patch.  Firstly, in my experience, I 100% need to protect my Libre.  Guaranteed it comes loose by day 14 without a doubt.  A full coverage patch for Libre is useful and will prevent sensor loss which can be costly.  Especially when exercising, in particular swimming and yoga.  A question that comes up regularly is “can I cover the hole” in the Libre.  There is some confusion around this one.  NJaP Patches are made of cotton, the same as your clothing.  For this reason, there is no problem covering the Libre with NJaP.  In reality, there is really very little issue with covering the hole and of the thousands of people wearing NJaP there’s never been any problems. 

Learn more about Finding the best adhesive to protect your Freestyle Libre sensor



About Rachel Baker, BNg, CDE, MNgPrac

Rachael Baker is a leading Nurse Practitioner Credentialed Diabetes Educator (CDE) in Brisbane and is passionate about staying up to date with Diabetes Technology and optimising these tools to be implemented in a way that is helpful and practical for people living with Diabetes. Using a holistic approach, Rachael focuses on self-empowerment for individuals living with Diabetes and supports them to live a life without limits.

About Pete Lomas, T1D 

Pete is the CEO and Founder of a diabetes technology start-up called Balance Health and the CEO of Not Just a Patch. As a person with T1D himself, he sees the opportunity in improving patient experiences via technology, product and brands. He is driven to make a difference in the lives of people with diabetes via design driven products and solutions.