Screen warnings
Bedside mode is meant to be left open on a bright screen for hours at a time, often overnight and while charging. Read this first.
Screen burn-in / image retention
Displaying the same bright image in the same place for long, repeated stretches — exactly what a full-screen bedside clock does — is a known risk factor for burn-in (permanent image retention) on OLED and AMOLED screens, common on most modern phones. This page's full-screen mode nudges the clock's position slightly over time as a mitigation, but that reduces the risk, it does not remove it. LCD screens are far less susceptible but are not risk-free either. If your device's screen already shows any ghosting or discoloration, stop using it in any all-night, static-display mode, including this one.
Heat and charging overnight
Bedside mode is designed to be used with your device plugged in so the screen can stay on. A screen running at full brightness while charging generates more heat than normal use. Don't cover the device (pillows, blankets, cases that trap heat), don't use a damaged cable or charger, and stop use if the device feels hot to the touch.
Follow your device manufacturer's guidance
alarm-clock.org doesn't know the specific engineering limits, battery chemistry, or screen technology of your exact device. Before leaving any phone, tablet or other device on and charging overnight, check your device manufacturer's own guidance on safe charging, screen burn-in / image retention, screen brightness, and extended or overnight use — that guidance is written for your specific hardware and takes precedence over anything general said here.
Disclaimer
This page is general information only, not a substitute for your device manufacturer's instructions, and not a guarantee that any particular device won't be affected by burn-in, overheating, battery wear, or other harm from extended or overnight display use. Using full-screen or bedside mode — or any other tool on this site — for extended periods is at your own risk. See our Terms of Service for the full liability terms.
See also browser timing limitations for why the alarm itself can't be guaranteed to fire on time in the background.