Ceiling Speakers as an outdoor speaker alternative
If you are seriously considering using ceiling speakers for use in the outdoors, without a doubt you have to first and foremost make sure that they are designed for outdoor use. Not only should there be sturdy and strong materials, the design should be able to withstand a multitude of weather conditions. Usually if a manufacturer develops an outdoor model more likely than never it will state and advertise that, but in the case that they don’t I wanted to give you a few indicators to look for that may help you differentiate them from other ceiling speakers. First of the cone portion will likely have a rubber edge, which of course is more weather permitting than their typical materials.
Normally the subwoofer and tweeters are made from a fine paper, outdoor ceiling speakers would not be constructed this way, for obvious reasons that we know how paper will react if water came in contact. Another issue we know with humidity, water and weather is that what it can do to metal. Yes you guessed it, RUST! This for sure is a big no no on speakers so be sure to make sure that the grills of the speakers are made with alloys like aluminum, stainless steel or at least at the bare minimal powder coated.
So you followed these tips, yet at the end of the day you have to realize you are putting your ceiling speakers out there in the outdoors, and you cannot expect the same life expectancy with a normal speaker but in the comfort of your own home. So like I mentioned here, water, humidity is not your friend, you can do precautions, but try to avoid installing ceiling speakers in areas with high water traffic, and ideally not in a extremely humid country!

Ceiling Speakers in an outdoor setting
Like I mentioned before having wide sound dispersion is very important when it comes to ceiling speakers. So imagine the speakers having to perform in the outdoors where there is no wall to bounce off from!! The reverb here is extremely high! So without a doubt, you would lose a lot of bass and treble, so especially in outdoor situation make sure that your ceiling speakers have a high bass/treble or at least have switches to boost them.
One final point that you have to be aware of is that, depending on how big your yard is and how loud you want your ceiling speakers to play before your neighbors call the cops, you would need a high power supply. So what this means is that you have to be aware that all the components in your setup has to be well designed to sustain that much power to give your speakers the best performance possible.