Replace the old and underpowered doorbell transformers for better performance. Compatible with Ring Pro and other smart doorbells like Nest (when connected directly to the video doorbell at 24 VAC/20 VA setting and not connected to a door chime). Not compatible with ring chime pro. UL Certified to guarantee safety and quality. Safe and easy install I on. WARNING: This product may expose you to chemicals known to the State of California to cause cancer or reproductive harm.