Notifications and alerts work by sending a message or email to your device when motion or sound has occurred. This feature is only found in the Wi-Fi monitors, and isn't the best feature for baby because it comes after the fact (sometimes up to 30 min or more after), it does not offer details of the type of sound or motion detected, and could get annoying with useless and excessive messages being sent. In the end, we prefer sound activation over notifications and feel that alerts and notifications aren't all that useful for keeping tabs on your baby.
It really depends on what you feel most comfortable with. There are audio monitors that allow you to listen to any noise coming from the nursery, vital monitors that track sleep and breathing and video monitors that add sight to sound. Babylist parents overwhelmingly choose video monitors. The security of seeing what your child is up to—like if they’ve gotten tangled in their swaddle, pulled their diaper off or climbed out of the crib—can be worth the extra cost of a video monitor.