Leave a clock on a phone propped against a monitor and it will be black within a minute. The device has no way of knowing that looking at the screen is the entire point, so it applies the same timeout it would to a page nobody is reading. A screen wake lock is the browser's way of saying otherwise, and it is a small request with a real cost attached.
This article covers what the Screen Wake Lock API does, which browsers support it, what keeping a display lit costs in battery life and panel wear, and when the sensible answer is to leave the setting alone. The fullscreen display mode is where this matters most, since it is the page most likely to be left running unattended.
What Does The Screen Wake Lock API Do?
It asks the operating system not to dim or switch off the display while the page is visible. A page calls navigator.wakeLock.request with the type set to screen, and if the request is granted the usual idle timeout is suspended for as long as that lock is held.
The API is narrower than it first appears, and the limits are deliberate. A screen wake lock only prevents the display sleeping; it does not stop the machine suspending for other reasons, does not keep a tab running in the background, and cannot override a manual press of the power button. It is released automatically the moment the page becomes hidden, whether by switching tabs, minimising the window or locking the device, which is why a page that wants to hold one across an interruption has to request it again when visibility returns.
Which Browsers Support Screen Wake Lock?
Support is broad but not universal. Chrome and Edge have supported the Screen Wake Lock API on desktop and Android for several years, Safari added it in version 16.4, and Firefox enabled it later than the others; a handful of smaller browsers still lack it entirely.
Two conditions apply everywhere. The page must be served over a secure context, meaning HTTPS, and the document must be visible at the moment the request is made. A page that tries to acquire a lock while hidden will simply be refused. Because support cannot be assumed, a well-behaved clock page treats the wake lock as an enhancement: it requests one, carries on regardless if the request fails, and never presents the feature as a guarantee that the screen will stay on.
What Does A Screen Wake Lock Cost?
Mostly battery, and on some panels a little longevity. A lit display is usually the largest single power draw on a phone or laptop, so holding a screen wake lock for an hour costs far more energy than everything the page itself is doing.
The costs are worth spelling out:
- Battery drain: the screen dominates power consumption on mobile devices, so a phone kept awake overnight as a bedside clock may well be flat by morning unless it is charging.
- OLED burn-in: static digits held in one place for hundreds of hours can leave a faint permanent ghost on OLED. LCD panels are not meaningfully affected.
- Heat: a device kept awake and charging at the same time runs warmer, and sustained heat is unkind to lithium batteries over the long term.
- Light in the room: a display that never dims is a nuisance in a bedroom or a dark studio, quite apart from the electricity it uses.
None of these is a reason to avoid a screen wake lock outright. They are reasons to pair it with low brightness and a dark layout, which cuts every one of them at once.
When Should You Use A Screen Wake Lock?
Whenever the screen is the output and nobody is touching the device. That is the whole test: if a person would have to reach over and wake the display to get the information they came for, the lock is doing something useful rather than merely burning power.
Clear cases include a countdown running in front of a class or a meeting, a phone on a bench during a workout, a tablet showing the time at a reception desk, a display beside a stage or a studio position, and any timing session where reaching for the mouse mid-count is unwelcome. A live countdown timer and a stopwatch with laps both fall squarely in this category, because both are read rather than operated. Related setups are covered in running a clock on a second monitor.
When Not To Use One
Leave the screen wake lock off when nobody is watching. A clock in a background tab, a laptop closing for the night, or a phone in a pocket gains nothing from a lit display, and on battery the loss is immediate and avoidable.
There are also settings where an always-on screen is actively unwanted. A bedside phone that never dims disturbs sleep. A device on a long journey with no charger needs every hour of battery it can keep. A shared meeting-room panel left permanently lit wastes power for the many hours a day nobody is in the room. The general rule is that a wake lock should be tied to an activity, requested when the session starts and released when it ends, rather than treated as a setting to be switched on and forgotten.
Alternatives On Fixed Displays
On a permanently installed screen, change the operating system's power settings instead. A system-level setting survives a browser crash, a page reload and a lost tab, none of which a screen wake lock does, which makes it the more robust choice for anything running unattended for months.
Set the display timeout to never, disable the screensaver, and on a laptop acting as a signage machine set the lid-close action to do nothing. Combine that with browser kiosk mode and autostart and the display recovers by itself from a power cut, which no page-level API can arrange; the full approach is in kiosk clock displays. Where the screen only needs to stay lit for a session at a time, the browser route is simpler and better mannered, and combining it with fullscreen gives a clean display in one step, as covered in getting a fullscreen clock in every browser.
Conclusion
A screen wake lock is a narrow, well-behaved request: keep the display on while this page is visible, and give the permission back the moment it is not. Support is wide, HTTPS is required, and the cost is battery life plus a small burn-in risk on OLED panels that low brightness and a dark layout largely neutralise. Use one when the screen is the output and nobody is touching the device, skip it when the display is idle, and prefer system power settings for anything permanently installed. Try it on the fullscreen display mode, or see the other displays on livetime.now.