Works for free chlorine in my shower. I tested the chlorine from my bathroom sink and shower faucet first using chlorine testing strips. It was pretty low to begin with apparently and then I tested the water coming from the shower head and the test showed a clear color meaning levels are undetectable (for this particular device). So, that's great news!!!

I tested it in hot water as some people had concerns saying it wouldn't work in warm/hot water (vitamin c and kdf filters are ineffective in hot water). I took a long shower (1-15 mins) and tested the water again right when I was about to be done and it still showed a clear sign(as opposed to the light blue color from the faucet). So, it seems that it is effective in hot water(not sure about kdf filters though). I don't know how it works for chloramines (common to be used alongside chlorine for disinfectant; its a combination of ammonia and chlorine) because my city doesn't use it in the water( I called and asked as well as looked up the water quality report.)