Bought one of these last year.
https://www.amazon.com/gp/product/B07DPFRT34/?tag=atomicindus08-20
You definitely can't run them while the house is occupied. In fact, you pretty much have to make sure the timer has expired for a few hours before re-entering the house. Even then, you'll still be able to smell the effect, and possibly have to air the house out before you are comfortable.
A few thoughts. Do they work? For the short term, it seems to. Long term I don't know. We smoke in the house and figured it was something good to run every once in a while, particularly if we know we're going to have guests over. If we were to sell the house, move out next month and ran it for a couple of weeks to eliminate smells, I just don't know if it would work long term.
When setting one of these units off, get out of the house immediately. I have found this unit to have an instant effect by the time my hand is off of the timer, and the smell is a "you can't breathe" potent. No running into the other room to grab a drink of water out the door, no grabbing keys you forgot. Turn it on and beeline for the door.
After letting it run for say two hours, and coming back 6 hours later, you're still going to smell the ozone effect. Seems to cover our house pretty effectively (3BR, 2 Bath). Again though, I don't know what the long term effect would be. We haven't had the chance to set it off and go on vacation for a few days and see if the effect still holds several days later with no further contamination introduced.
I discovered that many of these units are exactly the same from dozens of suppliers, they're just painted and labeled differently. The link I provided shows the cheapest price I could find at the time on that model.
One final note I have observed, is that prior to running it this past fall, we were getting the typical small spiders trying to come inside for the winter migration. The wife throwing a **** fit every time she'd run across one. After setting off the ozone generator for a couple of hours when we weren't going to be home all day, I noticed that ALL spider activity stopped. Haven't seen another all winter. So if nothing else, it seems to work pretty good as a pest control device.
