Pebble Smart Doggie Doorbell - 2-Pack - Blue Accent Include two transmiters and two receivers on the same frequency; can be used for one or two doors; great for larger or multi-level houses. Super easy installation, no wiring or tools required. One year manufacturer warranty. Built-in treat holder for easy and fun training. Positive owner and pet interactions. Detailed instructions included. Contact us if you need help. We strive to provide the best customer support. Volume control; Wireless, range up to 250 feet; Rain and snow proof; 36 selectable tunes