monitor

We have a Motorola Baby Monitor and really like it. It's easy to use, small enough to travel with, you can remotely adjust the camera angle, and it's a closed-circuit video signal that works throughout our house and yard. There are Internet-based monitoring systems that you can use on your phone and lots of people prefer those (Nest, for example). Some drawbacks of the Internet-based systems are that they can drain your phone battery and they are "pull" rather than "push" systems (as in you, you have to open the app to get the feed, as opposed to having it streaming on a dedicated monitor). You want to be able to hear the baby at night, so if you have a phone-based system, that means you need to have your phone on with the app open all night. I found that less attractive than a dedicated monitor with automatic screen dimming. That said, the Internet-based monitors have unlimited range, so you can check in on your baby while you're out at dinner or at work, whereas you can't do much with a closed circuit system if you go beyond your yard.

A brief moment of paranoia: there is some chatter that Internet-based monitoring systems can be hacked remotely (more here), which is one more reason I like having a closed circuit monitor.