No, your Wave monitor is always on and always measuring your indoor air quality.
The data collected by the Wave monitor is saved locally on the device and becomes visible in the Airthings app as soon as you sync your device again.
How Bluetooth syncing works
Just having your phone near your Wave monitor is not enough to sync.
In all, here's what you need to sync successfully.
Make sure your phone or tablet has Bluetooth turned on.
Hold you phone or tablet within Bluetooth range of your Wave monitor. Bluetooth range is within 33ft (10m) but the closer the better.
Open the Airthings app. If the app is not open on your device, syncing does not occur.
When your sync with the monitor, all of the measurements it has saved since the last sync are uploaded to your Airthings account in the cloud and available for you to see in the app or using the online dashboard at https://dashboard.airthings.com/
Wave Plus, Wave Mini, Wave Radon Gen 2 can save up to the last 80 days of measurements in their memory. Wave Enhance can save up to the last 130 days. It is important to not to allow it to go too long between syncing or you risk losing some past measurements. For example with a Wave Plus, if you don't sync for 100 days, you will have a gap in your history of about 20 days.
Note - If you are still having difficulties getting your Wave to sync even within Bluetooth range, we suggest you follow the troubleshooting steps here.