It is possible to locate a mobile phone without an app by using Google's Android Device Manager on an Android phone or by using Find My iPhone on an Apple phone. For these methods to work, the device must be connected to Google or Find My iPhone must be activated.
On an Android phone, it is possible to locate the device using Google's Android Device Manager if the device is connected with a Google account, the device has access to the Internet and the location services are turned on. To locate the mobile phone, navigate to the Google Android Device Manager tool on any web browser and log in with the same account the device is connected to. The location of the device is then displayed on a map.
On an iPhone, it is possible to locate a missing device by using Find My iPhone, if the service is enabled. To locate the mobile phone, log into iCloud using a web browser and your Apple ID. Click the Find My iPhone icon and an interface displays the location of the phone. If the location services have been turned off on the device, it is possible to activate Lost Mode and re-enable them.