Really not great, these work by startling the dog.
Long term, either the startle effect wears off and they stop working and you have to up the level of fear involved to get it to work again.
Or the aversive is too high and you scare the shit out of the dog which can trigger redirected aggression, cause a variety of incorrect association issues (was it the door that did it, the other dog that did it, the neighbour that did it...) or further stress/anxiety based problems. Which in Chi's particularly is likely to result in... more barking.
@tertrisnblox
Use management and counter conditioning.
Long lines fixed to harnesses whenever you open that door and you go out with them.
Pocket/pouch full of treats - the second they see something or hear a noise, you go nuts rewarding the experience, counter conditioning (like classical conditioning really!) - 'this = good stuff'. Mark the sound or sight with 'YES!' or 'noisies' or whatever word you want to use and scatter treats, stick treats up their nose pretty much... this needs to be dramatically exciting stuff. Not you standing there like a wet lettuce saying 'here nice doggy have a treaty'.
If they don't start hoovering up treats - you DO need to get the good stuff here, liver cake, sausage, cheese... no dry gravy bones or hard to chew boring stuff from the pet store within a few seconds, in you go without saying another word. The long lines allow you to do this without chasing or shouting.
You are not asking them to be quiet or behave.
You're not waiting to see if they bark at a thing you suspect will be a trigger.
It will be intense the first week, bit easier the second week, by week three you should find you can reinforce most stuff but not necessarily everything, by week four you should be able to reduce the number of treats and probably only use the long line on one dog (because when you, the treats and one dog go inside, so will the other).
It is hard work to start with if you're used to letting the dogs out unsupervised, and you DO have to do the same every single time, if you CBA sometimes and let them out off the leads and they go nuts and you have to chase about to get them in, you will undo the work you've done.
It does work though, and it doesn't matter if the dogs are nervous, if they're excited, or frustrated - nor does it teach them TO bark at whatever it is (because if that happens, they're looking at YOU when barking, the barkign is then designed to get you to hand over treats, and you can alter that easily. But in 20 years, it hasn't happened to me or any of my trainer colleagues!).
Once the four weeks is over you can generally drop to supervising fairly closely and treating particularly loud noises or sudden appearances of people. I'd maintain a random pattern of doing that forever, because it is pretty natural for Chis to bark at stuff.