Android: If you have an old Android phone or tablet lying around, Dormi is a new app that turns those old devices into smart baby monitors or remote speakers.
The video above shows you how Dormi works -- as long as your Android device is plugged in and Dormi is running, it will listen and transmit audio to your primary Android device. At any time, you can fire up Dormi on your primary phone, browse your other monitors, press one button to listen, press another to speak and have your voice played by the other phone, or just see what the ambient noise level is in the other room. The app works on your home Wi-Fi, or even over 3G/4G if the other devices are still connected to mobile data. For example, you could take your primary phone out and about, and use it on the go to listen in to your phones at home, which are connected to the internet via Wi-Fi. You can also see which devices you have set up to be "parent" and "child" devices using Dormi, what their battery levels are and how they're connected to the internet.
Dormi is technically a subscription-based app, but a one-time fee of $US7 lets you use as many monitors for as long as you want, indefinitely, so it's really just $US7. If you want to give it a try, you can download it, pair it with another device and use it for free for four hours a month, just to get a feel for it, after which the app will nag you to pay for it. Hit the link below to learn more and try it out.