1. The frequency used by this product complies with national regulations, does not cause harmful electromagnetic interference, and is universal. 2. It is convenient to install and remove the batteries outside the door, using 4 AAA batteries, and the indoor unit uses rechargeable lithium batteries. 3. The outdoor machine has a long working time, with 4 batteries up to more than six months. 4. The speaker is loud, the volume is adjustable, and the ringtone is changed, the sound quality of the intercom is clear, and it can be used for mobile intercom. 5. Long working distance, the maximum open distance is 200 meters. 6. Easy to install, directly stick to the wall with 3M glue. 7. Adopt learning code pairing, one outdoor unit supports N indoor units, without interfering with each other and without changing codes. 8. Exquisite, compact and beautiful. Size: 100*60*14.8mm