Kalenji ONrhythm 900 watch

REF: 8501811, 8501812, 8542938, 8542939



We have designed this watch for runners seeking a simple watch which measures the heart rate on the wrist and calculates calories. It helps you to learn to run at the right pace, feel good, increase endurance, lose weight and progress as a runner.

First use

How do i position my watch on my wrist?

Your ONRHYTHM 900 has an optical heart rate sensor to help you find the right pace when running. To guarantee precise heart rate readings:   - wear the watch with the face above your wrist - position the watch after the bone, in contact with your skin - adjust the strap so that it's tight but comfortable   The watch shouldn't turn or move on your wrist.

Kalenji ONrhythm 900 Putting your watch on correctly

How do i change the display when working out?

Once the heart rate monitor is on, you can change the display with the buttons at the bottom right and left of the watch (marked with arrows on the watch face).  3 displays: Display 1: Stopwatch and heart rate monitor Display 2: Heart rate and intensity zone Display 3: Time and calories burnt.

How are my intensity zones calculated?

Your intensity zones (warm-up, comfort, endurance, resistance and high resistance) are calculated automatically using your maximum heart rate.   These values are calculated by the watch according to your age and sex:  Warm-up: 50 to 60% of your max. HR Comfort (also called fundamental endurance): 60 to 70% of your max. HR Endurance: 70 to 80% of your max. HR Resistance: 80 to 90% of your max. HR (also called High Resistance): 90 to 100% of your max. HR

How do i change my maximum or resting heart rate?

You can manually set your maximum heart rate in the "Settings" menu, then "User"”. Confirm the proposed settings until you reach "max. HR" or "resting HR".

How do i manually set up a zone?

You can manually set up heart rate zones for running.A sound alert will inform you that you have left a zone.To set up zone alerts, go to the Settings menu, then Activity, then Zones. Select ON, then the minium and maximum values for your zone.To reset the automatic intensity zones (warm-up, comfort, endurance, etc.) select OFF.


Is the onrhythm 900 optical heart rate watch suited to all sports?

The technology in the ONRHYTHM 900 heart rate sensor is ideal for sports with repetitive movements such as running, walking, and working out on a cross-trainer or exercise bike.

Vibrations may cause errors. When cycling on a particularly uneven road or trail, you may notice variations in your heart rate.

You may notice errors when doing sports with unsynchronised movements such as fitness lessons, weight training, and racket or team sports

Does the onrhythm 900 optical heart rate sensor work on all types of skin?

The technology in the ONRHYTHM 900 heart rate sensor is designed for all skin colours and degrees of body hair. On dark or tatooed skin, less light is emitted by the skin. The sensor adapts by either injecting more light or adjusting the sensitivity of the light sensor. If, however, you do have a problem, contact our team with the button at the bottom of this page.

Why is my heart rate incorrect?

We chose the latest technology in the Philips sensor which is one of the most reliable sensors on the market. Some factors may, however, interfere with the heart rate reading:



The position of your watch must be adjusted correctly and be comfortable. If the strap is too loose, the watch will not be able to read the signal correctly.



If the back of your watch is dirty (soil, sun screen, etc.) the sensor may be less effective. Your ONRHYTHM 900 watch is watertight.You can wash it in clean water.



Readings made by the wrist-based optical heart rate monitor are optimal for sports with repetitive movements such as running and working out with a cross-trainer or exercise bike.

We recommend a chest strap heart rate monitor for fitness sports such as weight training etc.

To improve heart rate signal readings when you start working out, start it several minutes before your session so that it has time to search the satellites and your heart rate. Once you are ready, you can start the stopwatch.



- In cold weather, your blood vessels shrink which can be interpreted by the heart rate monitor as a low or high rate.



- The watch is a long way from your heart. The blood will a take a bit longer to reach your wrist. When interval training, the heart rate signal reading is delayed.



- You may observe errors in heart rate readings if you have tatoos on your wrist.



- The vascularisation on your right and left arm may be different. If results are not optimal on one arm, try the other arm.


How can i recharge my onrhythm 900 watch?

To charge your ONRHYTHM 900 watch, connect it with the cable provided to your computer, to a nomad charger or a 5V 1A mains adapter.

I have lost or broken my cable or my strap. where can i find a new one?

If you have lost or broken your cable or strap, please contact our technical team with the button at the bottom of this page.

Our tips

The heart rate in brief                                                            
How does an optical heart rate monitor work?                                         
Why run with a heart rate monitor?                                                           
How do i calculate my maximum heart rate?
How do i use a heart rate monitor?  
Understanding heart rate zones

I maintain my watch

- Cleaning the watch :
In order to keep your watch glass clean, it is advisable to clean it with a damp cloth.
In order to optimize the performance of the heart sensor, it is also advisable to clean it regularly with a damp cloth.

You can also clean the charging connector with a dry toothbrush

- Charging the watch :
You can charge your watch using the USB cable that came with your watch on a computer or any USB power outlet.

I repair my watch

The following repairs can be carried out on this product :

Bracelet change

The strap of your watch can be disassembled without tools by pulling the trigger on the pin of the strap.

To reassemble the bracelet, place the pin in the hole of the watch, pull the trigger then place the bracelet between the two lugs of the watch. Release the trigger and move the bracelet slightly to make sure the trigger is secure.

End of product life

If your product cannot be repaired, return it to a WEEE collection point or any DECATHLON store to optimize recycling.

Spare parts

Here is the list of spare parts for the ONRHYTHM 900 :

(currently no stock)


Here you will find the troubleshooting sheet for the ONRHYTHM 900.
By following the steps in this sheet, you can check if there is a possible problem with your product. If necessary, you will find in the "I REPAIR" section the tutorials indicated for the repair. You can also come to the workshops of your DECATHLON store.

Link to download the watch troubleshooting sheet (coming soon).

Workshop services

You want to entrust us with your product for repair. Here is the list of services offered by our workshops :

Used resale

Coming soon


  • Looking for the product instructions? Click here to download.

ONrhythm 900 Black

Would you like to contact us? access the contact form