From the manufacturer

Tips on product's operations

Simply connecting power for both units and allow 1-min for the units to link to each other.
Crystal clear sound with DECT 6.0 digital technology. The best reception can be obtained by placing units away from cordless phones or other electronic devices, and make sure the parent unit is 3 feet (1 meter) away from the baby unit.
You can choose to hear sounds from the baby unit all the time, or to hear sounds that exceed a certain VOX level. And set the parent unit to alert you with sound or vibration.
The parent unit is operated with the rechargeable battery or by AC power. A fully charged battery can operate 9 to 16 hours depending on monitor's sensitivity settings. As it takes up to 11 hours for the battery to be fully charged, turn the parent unit off while charging can help shorten the charging time.
The parent unit is preset to plays an audio Safety Reminder when it is connected to a baby unit. You may turn it off by pressing MENU / REMINDER / SELECT / OFF after your initial set up.

Other product features people love

A set of five LED lights on the parent unit indicates the level of sound in your baby's room so you can visually monitor noise level with the receiver muted. In vibration mode, the parent unit alerts you with gentle vibrations when your baby is fussing.

Talk from a parent unit to the baby unit (for DM221) and the other parent unit if you have two parent units (for DM221-2). You can use both of the parent unit at the same time to talk to the baby unit.

The loop on the baby unit illuminates as a gentle light night. Both your parent unit and baby unit allow you to turn on or off the nightlight. If no sound is detected for 15 minutes, the light will turn itself off.

Belt clip on the parent unit lets you hands-free and move freely around your home.

Digital Audio Monitor with two parent units with DECT 6.0 digital technology provides crystal clear transmission, eliminating the annoying white noise you hear from analog monitors. Extended Range Up to 1,000 feet of range allows you to feel safe and connected to your child while you go about your day. Talk-Back Intercom System Remotely communicate to your baby from the parent unit to the baby unit. Soothe your baby from another room or even from outdoors.