could you just put it in the room or would that not be as effective?

You could, but there may be hazards to work out.. Ozone (and the other products) damages plants and humans acutely, and chronically.. The variability of homemade units makes it impossible to estimate safety.. Ozone can be decently effective at fairly safe levels, but it can also be ineffective at dangerous levels.. If you do put in in the open make sure its near your exhaust window.. If you don't actively exhaust then I really don't want to suggest that..
Effectiveness is about the air mixing, and the best consistent way to do that is in ducting of some sort..

Sound advice my friend & worth me quoting,ozone generators are most effective & at their safest intended use when they are used in conjunction with a powered exhaust & passive intake set up,preferably with the generator mounted in a duct,as all mine are.

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My 4 day $40 bud dryer,http://www.rollitup.org/grow-room-de...ml#post2087235My DIY $3 Carbon filter,http://www.rollitup.org/grow-room-de...on-filter.html

And its really not tough to jimmy-rig electrodes into a duct.. An inline coffee-can rig could be made easily, but incase this isn't brutally obvious, make sure its all secure, and can't short out.. Any electrical short can start a fire, but HV is really good at it..
Oh, and always work with one hand behind your back if anything is live.. I usually glove one hand when working live.. On the otherhand, if this is actually new information for anybody regarding electrical safety then it'd probably be best to just buy a unit..

Do you think this would effectively get rid of the smell from one plant thats in a small locker in a garage?

No, it only works for huge commercial grows like 2000+ plants..

I know it will.

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My 4 day $40 bud dryer,http://www.rollitup.org/grow-room-de...ml#post2087235My DIY $3 Carbon filter,http://www.rollitup.org/grow-room-de...on-filter.html

I really like the way Ozone smells its like fresh rain. I like to clean out my car and use the ozone generator in it for a half hour or so it makes it smell soooo fresh.

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A garden of gratitude must first be cultivated in a mans soul before any seed will grow for him.Hydro Q's
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Be careful of its bleaching properties..

Isn't there any smaller models for micro/cab grows?
Can you make one thats small?