Pebble Smart Doggie Doorbell - Twin-Pack Best for both coming in and going out. Include two transmitters and one receiver, now with volume control. 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. Wireless, range up to 250 feet; Rain and snow proof; 36 selectable tunes