The collars were working when we initially got them. My cat and dog have been wearing them for approximately a month. We noticed the cat scratching a lot. Gave him a bath and he had a lot of fleas. My dog has had several ticks on her lately. I was trying to go natural but I guess I will have to get something from the veterinarian office. $80 dollars for two collars to work for a month was wasted money. I normally do not write reviews and do not like to harm a companies business but I do not want someone else to purchase a $39.00 collar that only works for a month.