Robot vacuums are interesting because the mistakes people make buying them are remarkably consistent. The person reads the suction power number, looks at the app features, maybe checks whether it has a mopping function, and clicks buy. Then three weeks in they realise it cannot get over the rubber threshold between the kitchen and the hallway, or it gets stuck under the couch, or the dustbin is so small it needs emptying every day.

None of these failure modes are hard to predict. They just require asking different questions than most product descriptions encourage you to ask.

Start with your floor, not the product

The single most useful piece of information about your home, for evaluating robot vacuums, is not the square footage. It is what the floor looks like at transitions between rooms.

Most robot vacuums handle flat hardwood or tile without difficulty. The problems start at edges. A standard rubber threshold between laminate and tile is usually around 12mm. Many mid-range robots top out at 15mm, so that threshold is fine. A slightly raised door sill at 18mm means that robot is now spending part of its cleaning cycle bumping against a transition it cannot cross.

Ask what the maximum threshold height is. Compare it to the actual thresholds in your home. This takes about five minutes and eliminates a meaningful subset of problems.

The carpet clearance question

If you have rugs, find out the underside-to-floor clearance of the robot. Low-pile rugs are generally fine. High-pile rugs can cause the device to either get stuck or ride up onto the rug and then fall back, which it will do repeatedly in the same cleaning cycle.

The relevant spec is sometimes called "obstacle height" and sometimes buried in the technical sheet rather than the main product page. A clearance of 10mm is about the lower limit for typical low-pile rugs. Above that starts getting uncertain.

There are three broad navigation approaches: random bounce, camera-based, and LiDAR. Most budget devices use random bounce — the robot moves in a direction until it hits something, then changes direction. This works but is inefficient, and the device may miss patches of floor in a session.

Camera navigation uses a forward-facing camera to build a map of the room. It works well in consistent lighting but can lose its bearings in darkness or bright sunlight depending on implementation.

LiDAR (laser-based) navigation builds a room map on the first pass and follows it reliably. It is more expensive and adds a small spinning tower on top of the device, which means the device will not fit under furniture lower than that tower height.

None of these is universally better. The choice depends on your home layout, your ceiling height, and how much furniture you have. A small open-plan flat might clean adequately with a random-bounce device. A larger home with many rooms will waste noticeably more time.

Dustbin volume and empty frequency

Robot vacuum dustbins are small. The typical capacity is somewhere between 400ml and 700ml. In a home with a shedding dog or thick rugs, a 400ml bin might need emptying after every session. That is a practical consideration worth thinking about before purchase.

Self-emptying stations — where the robot docks and the station empties the bin into a larger bag — are available at higher price points. They add cost and the replacement bags are a recurring expense. Whether that trade-off makes sense depends on whether you find emptying the bin genuinely annoying or just mildly inconvenient.

App dependence

Some robot vacuums require an active cloud connection to function fully. If the manufacturer's servers go down, or the company is acquired and the product line discontinued, you may find your device's scheduling and zone-setting features stop working. Local control — where the device works without cloud access — is a feature worth checking for if this concerns you.

This is not a theoretical risk. Several robot vacuum product lines have had their cloud services discontinued within a few years of launch.

A short summary of what to actually check

Before buying: measure your door thresholds. Note which are highest. Compare to the maximum obstacle height the device is rated for.

If you have rugs: check the device clearance height against your actual rugs. High-pile rugs need around 15mm minimum clearance underneath.

Decide what navigation type makes sense for your home. If you have a complex floorplan with multiple rooms, LiDAR is worth the premium.

Decide whether you want a self-emptying station. If you do not find emptying a small bin annoying, you do not need to spend more for one.

Check whether the device works without cloud access, if that matters to you.

The suction power number, the mopping function, and the app design are less predictive of long-term satisfaction than any of the above.