Check the number before you buy, because this is a genuine dealbreaker. Most robots handle a threshold up to roughly three quarters of an inch. Newer premium models climb higher — some near an inch and a half with a ramp or two-step assist.

Go measure your worst doorway right now

This takes thirty seconds with a tape measure and it saves people from a returned robot. Find the tallest transition in your house — usually a doorway saddle, a tile-to-carpet strip, or a sliding door track — and measure from the floor to the top of it.

Under three quarters of an inch and almost any robot manages. Between three quarters and an inch you’re into premium climbing hardware. Over an inch and a half and you’re outside what any consumer robot does reliably, no matter what the marketing claims.

If the robot can’t cross it, that room simply never gets cleaned. There’s no software fix for it.

The cheap workarounds

A rubber threshold ramp from the hardware store solves a lot of borderline cases for a few dollars. Look for a gentle slope rather than a steep wedge; the robot needs to get its front wheels up before its drive wheels arrive.

One thing that catches people out: a threshold the robot can physically climb may still stop it, because a dark or high-contrast strip reads as a cliff to the sensors underneath. If your robot is refusing a transition it should easily handle, that’s usually what’s happening, and it’s a different problem with a different fix.

Dad’s Take

Measure before you buy. This is the single most common reason a robot works everywhere except the one room you cared about.