A clock for your second monitor

The clock in your taskbar is about eleven pixels tall and sits in the corner you look at least. Meanwhile the second monitor is showing a chat window nobody has typed in since Tuesday. A full screen clock is a better use of that space, and it takes one keystroke — but the display will still go to sleep on you, and that part needs explaining.

The one-minute version

1. Open the clock in a browser window.
2. Drag that window onto the monitor you want it on.
3. Press F11 on Windows or Linux, or Ctrl+Cmd+F on macOS.

Fullscreen always applies to the display the window is currently on, which is why step two comes before step three. Get this backwards and the clock takes over the monitor you are working on.

Why the screen still sleeps

Your operating system turns the display off after a period with no keyboard or mouse input. It has no idea whether anything on screen is worth keeping lit — a video player, a dashboard, and a blank document all look identical to the power manager. Watching a film full screen does not trigger it because the video player explicitly asks the system to stay awake.

A web page can make the same request. The Screen Wake Lock API lets a page hold the display on for as long as it is visible, and it is what any clock worth using should be doing when you put it in always-on mode. Browser support:

• Chrome and Edge — version 84 and later
• Safari — 16.4 and later, including on iOS
• Firefox — 126 and later

Two constraints are worth knowing. The page must be served over HTTPS, so a clock opened from a local file will silently fail to hold the lock. And the lock is released automatically whenever the tab is hidden, then has to be re-acquired when it becomes visible again — which is correct behaviour, but means a clock buried behind other windows is not keeping anything awake.

What a wake lock cannot do

It holds the display on. It is not a general "keep the computer awake" switch, and it will not override:

• Closing a laptop lid
• Locking the machine manually
• A scheduled sleep or shutdown
• Enterprise power policy pushed by an IT department

If your screen still goes dark with a wake lock held, one of those is the reason, and no web page can do anything about it. A laptop driving an external monitor with the lid shut is the usual case — check your OS setting for what closing the lid does.

This is also why a clock should tell you whether the lock is actually held rather than assuming it worked. A page that says nothing and quietly fails is worse than one that admits the browser refused.

Getting the size right

A clock meant to be read from across a room and a clock meant to be glanced at over your shoulder are different sizes. A good rule for glanceable-at-a-desk is that the digits should be roughly the height of your palm at arm's length. Read from across a room, they want to be closer to the full height of the window.

A browser-based clock scales with the window, so you can tune this by resizing rather than hunting through a settings menu. Leave it windowed at whatever size reads well, then go full screen only when you want the whole display.

Leaving it on overnight

If the second monitor is OLED — increasingly common on laptops, still rare on desktop panels — a bright static clock left up for months can leave a faint permanent ghost. Use a dark theme, keep the brightness low, and prefer a clock that shifts its position slightly over time. The reasoning is worth reading if you plan to leave anything static on screen for long stretches.

On a normal LCD monitor this is not a real concern. Image retention on an LCD is temporary and clears on its own.

The alternatives, honestly

A browser page is not the only way to do this, and it is not always the best one.

• DisplayFusion (Windows, paid) gives each monitor its own taskbar with its own clock. Better if you want a clock and a usable second screen, worse if you want the whole display.
• Rainmeter (Windows, free) is endlessly customisable desktop widgets. Far more configurable than a web page, and far more work.
• Native widgets on macOS and Windows 11 will put a clock on the desktop, but it sits behind your windows and cannot fill a screen.
• A dedicated app is the right answer if you want alarms, timers, or something running without a browser open.

A web page wins when you want the screen filled, you want it working the same on every machine you sit at, and you do not want to install anything. It loses when you want the clock and other windows on the same monitor at once.

Open the clock and press Always On, or read about doing the same thing with a phone in a drawer.