I didn't invent the technique used but it's publicly available at http://www.creationkit.com/index.php?title=Detect_Player_Cell_Change_%28Without_Polling%29 and if it has any license I presume it's whatever content on the Creation Kit Wiki is licensed under. Otherwise I put any part of it I'm allowed to license myself into the Public Domain.
File credits
Bethesda, Unknown Author from creationkit.com, Pananacakes, exiledviper for PapyrusUtil, and the SKSE team for SKSE.
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Changelogs
Version 1.1
Removed unecessary distance-from-player condition that was breaking the mod in version 1.0
This utility mod takes the technique for checking when the player enters a new cell from the Creation Kit Wiki and puts the result in a handy variable that any script can access via exiledviper's PapyrusUtil SKSE plugin. The variable is a StorageUtil Int and acts as a counter that increments when a new cell is entered.
This is intended to help modders. If you use it in your mod make sure your users have it and PapyrusUtil installed too.
Note: I uploaded a bum version the first time. New upload version 1.1 should be right. Sorry about that!