That old phone in your junk drawer is not junk. It is a free security camera. I turned my retired phone into a dedicated monitor for the back porch, and it works better than the cheap camera I bought for the same job.

Here is how to set it up in about twenty minutes.

What you need

Any smartphone that still turns on works, even one with a cracked screen. You also need a charging cable and a Wi-Fi connection. That is the whole shopping list. The phone does not need a SIM card or a phone plan. It just needs power and internet.

Pick an app

There are several free apps that turn an old phone into a camera. I use one that streams over the local network, which means the video stays inside my house and does not go through some company’s server. Look for apps that let you view the feed from another device, like your main phone or a tablet.

Two things to check before you commit: make sure the app supports background streaming, and check if the free tier puts a watermark on the feed. Some apps are free only for a limited time, so read the fine print.

Position it carefully

Place the phone where it gets the view you want and where it can stay plugged in. The main limitation of a phone camera is the field of view. It is wide, but not fisheye wide. Test the angle before you mount it. I set mine on a shelf facing the back door, and I checked the feed on my main phone to make sure it actually caught the whole entryway.

Deal with the battery

A phone running a camera app 24/7 gets hot and the battery swells over time. Two fixes: remove the battery if you can, or keep the charge limited. Many phones let you cap the charge at 80 percent in the battery settings. Some apps even have a setting to stop charging at a certain level. A phone that runs hot all day will not last forever, but it will last a lot longer with these settings.

Set the screen to stay off

Turn the screen brightness to minimum and let the screen sleep. The app keeps recording in the background, and a dark screen means less heat and less power. I also turned off notifications on the old phone so nothing pops up over the feed.

My old phone has been running as a porch camera for four months now. It cost me nothing, it is out of sight, and I can check the feed from my main phone any time. Before you buy another security camera, check your junk drawer.