The more u spend on a thermal imager the happier u will be. They can't see through glass ! They have a hard time with heavy foliage. Anything in the water
that's the same temperature will be invisible. If you want to see people through solid walls then you'll need to spend tens of thousands of dollars ! The only way to find out is borrow or buy one and try it out. I like mine cuz of other reasons. Like how it shows in picture mode all the temperatures in colour when pointing it at my breaker panel with the cover off or checking for hot spots on my engine
with a glance at the image.