Baby monitors split into three types that differ in a genuinely important way: how the signal actually gets from the nursery to you.
The three types
Audio-only monitors transmit sound over a short-range dedicated radio signal between two units, with no video and no connection to the internet at all — the simplest, most private option, well suited to a nursery close enough for a dedicated signal to reach reliably.
Closed-circuit video monitors add a camera and screen, but still operate over a private, dedicated signal between the camera and the parent unit only, not over home Wi-Fi or the internet. This keeps the same basic privacy profile as audio-only while adding the visual reassurance many parents want.
Wi-Fi-connected "smart" monitors stream video through your home internet connection, letting you check in from a phone app anywhere, including away from home. This is genuinely convenient, but it introduces a real security consideration a closed-circuit system doesn't have: an internet-connected camera is a device that could potentially be accessed by someone other than you if it isn't properly secured.
If you choose a Wi-Fi monitor, take security seriously
Change the default password immediately, use a strong and unique one, and enable two-factor authentication if the manufacturer offers it. Keep the device's firmware updated, since manufacturers do patch real security vulnerabilities discovered over time. There have been real, documented cases of poorly secured smart baby monitors being accessed by unauthorized parties — this isn't a hypothetical risk, and it's specifically a tradeoff that comes with the added convenience of internet connectivity, not a flaw in baby monitors generally.
Range and interference matter more than expected
Even non-Wi-Fi monitors can pick up interference from other household electronics operating on similar frequencies, and range claims on packaging are typically measured in open, obstruction-free conditions — real range through walls and floors in an actual home is often meaningfully shorter. If the nursery is far from where you'll typically be, checking real-world range reviews for a specific model is more useful than the manufacturer's stated maximum range.
The one thing people forget
Check the battery life of the parent unit if it's meant to be carried around the house, not just the camera unit's power source. A camera that's always plugged in doesn't need to worry about battery life, but a parent unit that dies partway through the day defeats much of the monitor's purpose.