NOTE: Tesla is starting to release an update (2020.12.5) with an in-car Dashcam / Sentry viewer that you can use on the car's screen. If you have that update and you just want to view your Sentry videos, you don't need this app! But the app provides some functionality beyond what the in-car viewer has:
-Faster and slower playback speeds (.25x to 16x)
-Skip to the Sentry event trigger time
-Share and Save clips
-Create composite videos that merge multiple cameras into a single video to share/save

With this app you can easily view the dashcam or Sentry Mode videos saved by your Tesla vehicle on your mobile device by removing the USB drive from the car and plugging it into the device with an adapter. These adapters are often called OTG adapters and sometimes come in the box with your phone.

Keep the adapter in your Tesla vehicle and anytime you get in the driver's seat to a notification saying "Sentry: 4 events recorded" you can pop out the thumb drive and look at the videos. Just make sure you hold down the camera icon on your vehicle's screen to ready the USB drive for removal.

If you're in an accident or a victim of a theft or vandalism, this tool can help you zero in on the relevant videos and share them with law enforcement.
From version TeslaCam / Sentry Reviewer 1.3.3:
Streamlined playback UI so there is less tapping to show and hide controls
Added icons to show which events have already been viewed
Added ability to save custom videos (premium)
Bug fixes
All versions