This type of monitoring device attaches to your baby via their diaper, clothing or as a sock depending on the model. Most of the wearable options alert in the room and only a handful send a message to a parent device (smartphone or similar). In our experience, many of these have high false alarms from moving and crawling babies or high Electromagnetic Field (EMF) Levels (which we try to avoid). The Snuzo Hero SE is a cost-effective wearable with a unique vibration feature and very low levels of EMF.
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.