FOR BEST CONSTANT SUPPORT: Use only FELIWAY diffusers with FELIWAY refills. Refills last up to 30 days and should be replaced when empty. The diffuser device should be replaced every 6 months. Best results are seen after 3 to 4 weeks of continuous use though some cats show improvements within the first 7 days. Degree of results may vary. EASY-TO-USE: Plug in an open area where your cat spends the most time. Due to size, it's recommended to use an outlet free of any other devices. Each diffuser is scentless, with no affect on humans or other pets, and covers approximately 700 sq ft. Leave plugged in continuously with 4ft of clearance above. Note: when operating properly, the diffuser device will get warm to the touch in addition to a green indicator light turning on. MORE EFFECTIVE COMPREHENSIVE: Supported by 25 clinical papers, FELIWAY Optimum resulted in 93 of cat owners reporting enhanced calming in their cat and an average satisfaction rating of 9.1 10. All thanks to FELIWAY Optimum's newly discovered and patented Feline Pheromone Complex, helping in both single-cat and multi-cat situations. Scentless, with no affect on humans or other pets. SAFE VET-RECOMMENDED EXPERTISE: For over 25 years, the range of FELIWAY cat pheromone products have helped more than 14 million cats worldwide, thanks to FELIWAY's expertise in cat stress, and innovation in cat calming. BEST CAT CALMING CHOICE: From FELIWAY, the makers of the original vet recommended cat pheromone diffuser, FELIWAY Optimum is for cat owners wanting the best for their cats: it calms cats better than ever and reduces more signs of stress in more situations.