IDK if that's true, I have one that I paid about $100 for and has sensing. It's quite nice and I basically never know when it's on it's so quiet. It also came w

IDK if that's true, I have one that I paid about $100 for and has sensing. It's quite nice and I basically never know when it's on it's so quiet. It also came with a reusable/washable filter, so I've never had to replace it after about 3 years of use now. Any ways, I DIY a lot of stuff, but there's not enough interest in this one unless you're just a glutton for frugality or find some interest in this particular project. My point was that for most people this would be a negative time value of money for inferior outcome; which I think are why most people DIY things... so they can afford better or learn something. (There is no learning when all you're doing is strapping a filter to a box fan.)