Solid state USB rechargeable air freshener.

This style of unit isn't new, but this is one of the neatest implementations I've see.
It's an air steriliser for small areas like cupboards and fridges (but not freezers).

It works by generating a high voltage inside in a well potted module that is probably a classic Royer oscillator, step up transformer and probably a voltage multiplier too based on external test results.
It applies the high voltage to a sharp spike like an ioniser, but instead of imparting a charge into the room it has a metal ring in front of it at the opposite polarity that attracts the emitted ions so vigorously that it creates a small corona discharge at the tip of the spike. The high flow of electrons also causes a movement of the air in the vicinity causing a noticeable draught from the front of the unit with no moving parts.

As the air passes through the corona discharge oxygen molecules (O2 = 2 atoms of oxygen) are split apart into individual oxygen atoms that recombine randomly, producing a small quantity of ozone (O3 = three atoms of oxygen). Since ozone is an unstable form of oxygen the molecules try and get rid of the third atom of oxygen onto anything it touches, oxidising it in the process.

This has the effect of a gaseous form of bleach which can get rid of organic smells while also damaging mold spores, bacteria and viruses. When placed in a fridge the unit will neutralise odours and help keep food fresh for longer.

This unit has a 500mAh lithium cell that can be recharged using a standard micro USB connector. When in use the unit runs continuously for 30 minutes to give a strong initial sterilisation, but then goes into a top-up mode where it runs for 5 minutes every hour.

The construction of this gadget is surprisingly good. It's got a very nice case and everything is laid out sensibly inside with proper support for an easily removed lithium cell, and plugs for the PSU, cell and front panel button. The circuitry is fairly sensible and the actual operation in my fridge immediately neutralised the smell of strong out of date cheese.

Based on the operating current and near zero current in its off-state I initially estimated the run time to be over a week on a charge. Unfortunately the software is not putting the processor to sleep during standby, so the quiescent current between the hourly bursts of ozone is around 2mA. That might not sound much, but it almost doubles the daily power use and means the run time is going to be nearly half of what it could have been. If the processor has an internal wake timer then it could have woken every second or two, pulsed the LED and then gone back to sleep again, doubling the operational time per charge.

The ozone output will also fall as the lithium cell discharges and its voltage drops. So the main clue that it's time for a recharge could be the natural aroma of a fridge.

It's notable that the unit will not run while plugged in to recharge. That seems a strange thing to do, since they actually added extra components to detect that, and it could have been useful to have it running 24/7 in a larder. But it can be hacked.... Even solar-charged if the sense circuit has the 10K resistor removed.

You can find these on eBay if you search for - USB rechargeable ozone . But be aware that there are still a lot of pandemic price gougers around, so the target price is $20 or less. If you can't find it near that then leave it for a while until prices return to normal.

Sharp use the same technology to produce very small levels of ozone in their plasmacluster products, which they then mix into the air with a quiet but powerful fan. (They specifically avoid mentioning that their units create trace ozone.) Since the Sharp units are designed for long operation in large areas they have replaceable cartridges with new power supplies and emitters in them, as the tips of the spikes can be blunted over time by the action of the corona discharge.

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