For the technical requirements to install and use the app, see here.
You can find all the SmarTracks Locations here.
No, you can use the app without a DX5.0 sensor. You do need to have access to a SmarTracks Location. These locations have Timing Gates integrated under the surfaces, which your phone’s sensors will detect. To see whether the app can run on your smartphone, see the technical requirements.
To ensure good Timing Gate detection and step recognition with your smartphone, you need to wear the phone on your lower back while running. You can find suitable running belts for this here.
If you want access to livestream results and other features, you need a DX5.0 sensor.