You wipe the dust, you close the window, you buy the machine, and you still have no idea whether any of it worked.

Put this on the bedside table and the guessing ends. Eight readings, live on screen, so you can watch what actually happens to your air when you light a candle, close the door, or switch the purifier on.

It settles arguments. Light a scented candle next to it and watch the particle count climb inside a minute. Open the window on a high pollen day and watch it climb again. Nothing about your air stays a matter of opinion once there's a number on it.

It tells you whether your purifier is earning its place. People already buy monitors for exactly this reason: to audit the machine they've paid for. We would rather you did that with ours than spent three years wondering.

Eight readings, live on screen. CO2, PM2.5, temperature and humidity among them, updating continuously, readable from the other side of the room.

Humidity counts too, in a British house. That number matters as much as the particle count here, because damp is what turns a cold north-facing bedroom into a mouldy one over a single winter.

The screen is the product. No unlocking, no scrolling, no waiting for a connection to tell you what the air in front of you is doing.

For anyone who has bought something to fix their air and never quite known whether it worked, and for anyone who would rather find out than be told.

• Readings: eight, live and continuous. CO2, PM2.5, temperature and humidity among them
• Display: colour screen, readable across a room
• Placement: bedside table, desk, nursery shelf
• Power: rechargeable, no wiring

£129. Free UK delivery and free returns · 30-day risk-free trial.

Run the candle test on your first evening with it. If the number doesn't move, send it back and we'll cover the postage.