It's pretty slow going down they have plenty of time to get out of the way. There is no sensor to keep it from going down, but if there is something in its path, it stops because it can't go down further. Also, if that happens, it goes back up because it can't complete the "circuit" that its programmed to do. I've had mine for 3 yrs. with no issues. The only thing that could be an issue is that in the winter, the battery runs down quicker once those temps drop, so it's not as fun replacing it when that happens. I usually replace at the beginning of winter, but it always seems that with my set up and conditions, I find myself replacing mid winter as well. With that said batteries are affected by extreme weather conditions when used outdoors.