Why WHOOP and Fitbit need your phone unlocked

Both devices stop broadcasting when the phone screen locks. Change auto-lock for the session, then put it back.

WebiPhoneAndroid Updated 26 July 2026

What this does

Explains why your heart rate goes quiet a minute after you put the phone down, and what to change.

Sentinel reads physiology through a Bluetooth link to the strap. WHOOP and Fitbit Air both stop serving that link once the phone screen locks. The session keeps running, the timer keeps counting, and no readings arrive, so no rule can fire. Sentinel goes silent exactly when you stop paying attention to it, which is the worst possible time.

The chest straps and the Polar Verity Sense do not have this problem. They keep streaming with the phone locked and the screen off.

VEXA shows a notice about this each time you start a session on one of the two affected devices, and the notice includes the setting to change.

Before you start

This is a device behaviour, not a VEXA setting. There is no switch inside VEXA that fixes it.

Leaving a screen on all day costs battery and, on OLED phones, is not ideal for the display. Keep the phone on a charger while you trade, and put the auto-lock setting back afterwards. The notice says the same: you can revert the setting after your trading session ends.

If neither of those trade-offs appeals, the answer is a different device. A Polar H10, a Garmin HRM-Pro Plus or a Polar Verity Sense all work with the phone locked, and all three also give you live HRV, which WHOOP and Fitbit Air do not.

Steps

Start the session from the web as normal.
Read the unlocked-phone notice and click Understood.
Change the setting on the phone that holds the strap, using the iPhone or Android steps in the other tabs.
Leave the VEXA app open on that phone with the screen on.

Open the iOS Settings app.
Go to Display & Brightness > Auto-Lock.
Choose Never.
Open VEXA and start your Sentinel session.
Set Auto-Lock back to your usual value when you finish trading.

Open the Android Settings app.
Go to Display > Screen Timeout.
Choose the option that keeps the screen on.
Open VEXA and start your Sentinel session.
Set the screen timeout back when you finish trading.

What you should see

A beats-per-minute figure that keeps updating while the phone sits on the desk, and a LIVE badge that stays lit rather than dropping out after a minute.

If you check the live chart at the end of the day it should be a continuous line, not a series of short segments with gaps between them.

If it doesn’t work

Readings still stop when you look away. The phone dimmed rather than locked on some Android skins, or a battery saver overrode the timeout. Check the battery settings and exclude VEXA from optimisation.

Gaps appear in the chart even with the screen on. The strap moved out of range, or another app grabbed it. Bluetooth range through a body is short, so keep the phone on the desk in front of you rather than in a back pocket.

You do not want to leave the screen on. Switch to a chest strap or the Verity Sense armband. See Which heart rate devices work.

Set up WHOOP for Sentinel Turn on Heart Rate Broadcast in the WHOOP app, pair the strap to VEXA over Bluetooth, and keep the phone screen on while you trade. Set up Fitbit Air for Sentinel Turn on Share Heart Rate and Extended Pairing in the Google Health app, then pair the Fitbit Air to VEXA over Bluetooth. Which heart rate devices work with Sentinel The seven wearables Sentinel supports, how each one connects, which ones need your phone unlocked, and which ones can measure HRV.

Still stuck? Email support@vexatrade.ai.