Caffeine for Windows: a classic, honestly aged.
Zhorn Software's Caffeine has kept Windows PCs awake since around 2010: a tray icon that simulates an F15 keypress every 59 seconds. It still works, it's still free, and for some people it's still the right answer. Here's what that keypress trick actually implies, and what the tools built since do differently.
How Caffeine works — and why it matters
Windows decides your PC is idle when no input arrives and no program asks to keep it awake. There are two ways to interrupt that: simulate input, or use the power request API Windows provides exactly for this purpose (the same one your video player uses so the screen doesn't dim mid-film).
Caffeine takes the first route: every 59 seconds it presses F15 — a key your physical keyboard doesn't have, so most apps ignore it. It's a clever 2010 trick, and its side effects are the reason people go looking for alternatives:
- Some apps don't ignore F15. Full-screen games, remote-desktop sessions, some terminal emulators and old tools can react to the phantom key — from cancelled screensavers to weird input in the wrong window.
- It's all or nothing. Caffeine is on or off. No "for 2 hours", no "while this app runs", no schedule — you toggle it and you remember to toggle it back.
- The simulated keystroke is visible to software. Windows flags synthetic input as injected. Usually irrelevant for keeping a PC awake, but it's a fact worth knowing.
The modern way: ask Windows politely
Tools built since — Microsoft's PowerToys Awake, StayUp — use the power request API instead: no fake input at all, just a standing request that Windows itself honours. The PC stays awake (and optionally the display stays on), nothing is typed anywhere, and the request disappears the moment the tool says so.
Side by side
| Caffeine (free) | PowerToys Awake (free) | StayUp ($8.99) | |
|---|---|---|---|
| Method | Simulated F15 every 59 s | Power request API | Power request API |
| Keep awake for a set time / until a clock time | — | Yes | Yes, favourites one tap away |
| Per-app rules (“while Zoom runs”) | — | — | Yes |
| Daily schedule | — | — | Yes |
| Optional stay-active nudge | Its keypress is one, always | — | Optional, off by default |
| Footprint | Tiny single exe | Part of the PowerToys suite | One portable exe, no admin |
| Last meaningful update | Years ago | Actively maintained | Actively maintained |
| Price | Free | Free | $8.99 one-time · 3-day free trial |
Checked in August 2026. Caffeine's simplicity is genuinely part of its appeal — this table isn't a eulogy.
Keep Caffeine if…
- You've used it for years, it has never misfired with your software, and on/off is all you need. Don't fix what isn't broken.
- You need something that runs on ancient Windows versions modern tools have dropped.
Switch when…
- The phantom keypress ever bites — a game menu that flickers, a remote session that catches F15. The power API route simply has no input to catch.
- You keep forgetting to toggle it. Durations, per-app rules and schedules exist so the tool remembers instead of you. That's the whole idea behind StayUp.
- You want "awake" and "active" as separate, deliberate choices. StayUp keeps the PC awake via the API, and only if you enable it adds a stay-active nudge for idle-based status dots — your call, off by default.
Verdict. Caffeine earned its place, and if it still fits your use, keep it. If you want durations, rules and schedules instead of a toggle you have to remember — try StayUp free for 3 days and see whether the difference matters in your week.
3-DAY FREE TRIAL · ONE-TIME · 2 PCs · 14-DAY REFUND · WINDOWS 10/11