That old phone in your drawer is not obsolete. It is a security camera waiting for a job. I turned my retired phone into a baby monitor for my daughter’s room and later into a front door camera, and it cost me exactly nothing beyond what I already owned.

What you need

Any smartphone from the last eight years or so works, plus a charger cable long enough to reach an outlet and a free camera app. Alfred and Manything are the two apps I have used, and both run on Android and iOS. You install the app on the old phone and on your current phone, sign into the same account on both, and the old phone becomes the camera you can watch from anywhere.

Set it up where the view matters

Place the old phone where it has a clear view of the door, the crib, or the hallway. Angle it down slightly so it sees the whole area, not just the ceiling. Plug it in and keep it plugged in, since camera mode drains battery fast. Turn off sleep mode in the phone settings so the screen does not lock and stop the camera.

Make it actually useful

The apps include motion detection and alerts, which is where the magic is. You get a notification on your main phone when something moves, and you can watch live or review clips. Many apps also let you talk through the phone, so it doubles as an intercom. Test the alert delay before you rely on it. My first setup sent alerts about twenty seconds late, which mattered for the front door.

Things I learned the hard way

• Use a short, thick charging cable. Long thin cables can drop power and the phone dies at the worst time.
• Keep the old phone updated with the camera app before you mount it, because updating after is awkward.
• Point it away from windows at night, or the infrared can glare.
• For outdoor use, place it inside a window looking out, not exposed to weather.

The old phone approach is not as polished as a dedicated camera, but it is free and it works. Mine has run for months with zero problems, and when the phone finally dies, I will just grab another retired one from the drawer.