iRobot Roomba Plus 515 Combo

Suction in pascal, as the maker measures it. More pascal helps on carpet, but it says little about how well the robot picks grit off a hard floor.

A brush that guides hair to the side instead of letting it wind around the shaft. It saves the cutting work in homes with long hair or pets.

The side brush swings out in a corner or along a baseboard, so the dust there is swept in too. On this model: from the maker's product text, not from a specification table

How the mop is built: flat pads, two spinning discs or a roller. Discs press harder on dried-on dirt, a roller rinses itself while it works.

How far the robot lifts the mop when it drives onto a carpet. From about 0.4 in (10 mm) a medium pile stays dry.

The pad slides out along a wall or a baseboard, so the last few inches are mopped as well.

The robot leaves the mop at the dock before it vacuums a carpet, so the carpet never gets wet. On this model: the maker names this feature nowhere on the product page, so we take it as no

The robot returns to the dock during a run to rinse the mop, instead of pushing dirty water around.

The dock empties the robot’s dust bin, usually after every run. You only empty the dock’s bag or bin.

The dock collects dust in a bin instead of a disposable bag. No bags to buy, but you empty it yourself. On this model: the maker names this feature nowhere on the product page, so we take it as no

How long the maker says a dust bag lasts with daily use. With pets or a lot of carpet it is shorter.

The dock washes the mop for you, so you do not rinse it by hand. On this model: from the maker's product text, not from a specification table

How hot the dock washes the mop. Above 140 °F (60 °C) grease comes off, which is what keeps a mop from smelling.

The dock dries the mop afterwards, so it does not sit there wet and start to smell.

Drying is done with warm air instead of cold. It is faster and it helps against smell.

The dock mixes detergent into the water itself, from its own bottle.

The dock can be connected to the tap and the drain, so you never fill or empty a tank. It does need a connection nearby.

The width, depth and height of the dock. Measure the spot you have in mind, and leave room for the lid and for the robot driving in.

How the robot maps your home and follows that map. Lidar measures with a laser and works in the dark, a camera looks along and recognizes more. On this model: from the maker's product text, not from a specification table

How the robot sees loose things on the floor, such as cables, socks or a pet accident. A camera with depth sensing sees more than a bumper that reacts on contact.

An extending leg or wheel that carries the robot over a high threshold. Without one it usually stops at about 0.8 in (2 cm). On this model: the maker names this feature nowhere on the product page, so we take it as no

How tall the robot is. It decides whether it fits under your sofa, bed or cabinet.

How wide the robot is. Narrower gets between chair legs more easily, wider usually means a bigger dust bin.

What the robot weighs. It counts most if you carry it up a staircase every day.

The capacity of the battery. It hints at the runtime, but how much the robot draws counts just as much.

How long the robot cleans on one charge, at its quietest setting. After that it recharges and carries on where it stopped. On this model: from the maker's product text, not from a specification table

Matter is the standard that lets devices from different makers work together. With it you can run the robot outside the maker’s own app. On this model: the maker names this feature nowhere on the product page, so we take it as no

Which voice assistants the robot works with, such as Google Assistant or Alexa. On this model: from the maker's product text, not from a specification table

The warranty the maker gives in the United States.