Window guards vs window stops: bars across the opening, or a block in the track

What each one does

A window guard is a set of steel bars, spaced under 4 inches, that screws into the window frame across the opening; the window opens fully for air and the bars stop a child. A window stop is a small block that attaches to the frame or the track so the sash physically cannot slide past it; the window opens the few inches you set. The CPSC recommends both in the same breath: install window guards, and install stops so windows open no more than four inches. It estimated 5,600 children treated for window falls in 2024 and counted at least 25 deaths from 2021 to 2023. The full product ranking is best window guards and locks.

Side by side

Egress: the question that decides bedrooms

A bedroom window is a required fire exit in most US building codes. A guard bolted across it turns the exit into a wall unless the guard has an emergency release, which is exactly what ASTM F2090 requires for guards sold for single-family homes and lower floors; the CPSC pressed for that standard in 2000 after children died behind guards in fires. Guardian Angel states F2090-21 and describes release buttons on its guards. A stop has no egress problem, because an adult can pull the Window Wedge off its Velcro or switch KidCo's lock back in a second; that is also its weakness, because an older child can do the same.

Which windows each fits

Double-hung and single-hung: either; a stop on the lower sash, or a guard across the opening. Horizontal sliders: a track lock (KidCo) or the Window Wedge in the track, or a guard installed vertically, which Guardian Angel's page allows. Casement (crank-out) windows: a guard, or remove the crank handle; a stop has no track to sit in. Sliding patio doors: the track lock, plus a door alarm if the door leads to a pool. Type by type, with the install, is how to childproof windows.

Choose a guard if / choose a stop if

• Choose a guard if the window is above the first floor, the child can reach the sill or has furniture to climb, you want to open the window wide, or it is a casement.
• Choose a stop if a 4-inch opening is all you need, the window is hung or sliding, and you want it done in a minute without a drill.
• Choose both if the window has a low sill in a toddler's bedroom: a stop for daily use, a guard for the day you open it wide. And move the crib away from it regardless.

Neither a stop nor a standard guard behaves the way you expect on a casement, because a crank window has no track to block: that case is on how to childproof casement windows.