Presence, which was launched late last month, converts a spare Internet-connected iPhone, iPad or iPod Touch into a free video camera with real-time video and audio streaming, and motion detection and notifications.
"Essentially we give you an inexpensive security system that you can use to monitor your house, or help you watch your kids, cats, elderly relatives or act as a baby or nanny cam," said Gene Wang, chief executive of the Palo Alto, California-based company People Power.
Unlike traditional monitoring systems that can be expensive and need technical knowledge to install and use, Wang said Presence is a free do-it-yourself system that can be set up simply by downloading and configuring the app.
To use it consumers install and login to their account on two devices - for example two iPhones. Then they can start the camera within the app on one of the devices and it can be viewed from the app on the other.
Triggers can also be set to record when motion is detected and to send alerts. The app can help to avoid false alarms, according to Wang, because it sends a video clip in an email to the user showing the motion that triggered the alert.
"With these high-end security systems, you have a lot of false positives and then the security company and police come out and it turns out it was your cat knocking over a broom or something like that," Wang explained.
He added that many people have replaced their old smartphones with new ones and a monitoring system would be a good way to make use of the old devices.
Another app created by a company called People Power 1.0 for iPhone and Android reads electricity meters in real time to show consumers how much they're spending and whether they are going over budget.
"The center of computing has switched to these smart computers that we all carry in our pockets," Wang explained.
"What people are going to want to be able to do is control their personal Internet of Things from their hands," he added, referring to Internet-connected devices in the home.
The company also plans to work with underfunded public schools to help them set up security systems using old devices donated by the community.
Other apps have similar functions. AirBeam is a home monitoring app for iOS that allows users to access video feeds from a Web portal.
Izon is an app that streams real-time audio and video from iZon cameras to iPhone and Android devices, and Ivideon, for iOS and Android, also lets people build their own surveillance system.