Good question ! The free version is a complete single-camera dashcam: loop recording that never fills your storage, automatic clip lock on impact, speed overlay, gallery, and watching another Sentinel phone live is free too !

Pro adds:

• Both: road and cabin recorded at the same time (on phones that support two cameras at once)
• Remote access: watch this phone live and browse its clips from your other devices
• Cloud offload: clips copied to your NAS, WebDAV or a cloud folder
• Periodic snapshots: a still picture every few minutes
• Push notifications via ntfy

It will be a one-time purchase, planned around 5.99 (Google converts it to your local currency). No subscription, no ads. With the tester code SENTINEL-BETA you get Pro free for 30 days.