Set it up once, forget about it. Every morning your lockscreen updates to the next day of the challenge. Works on iPhone and Android.
Download the 21 wallpapers
Click “Download All 21” above. Save all images to your Photos app (or create a dedicated album called CMM Challenge).
Open the Shortcuts app
Go to the Automation tab at the bottom. Tap + New Automation.
Choose “Time of Day”
Set it to 6:00 AM (or whenever you want). Select Daily repeat. Choose “Run Immediately” (not “Ask Before Running”).
Add actions to the shortcut
Add these actions in order:
a) Get Current Date → format as custom: d (day number)
b) Find Photos where Album is CMM Challenge, sorted by Name, limit 21
c) Get Item from List → Item at Index = the day number variable (use modulo 21 if you want it to loop)
d) Set Wallpaper → choose Lock Screen → set to the photo from step c
Alternative: Simple version
If the above feels complex, use the simpler approach:
a) Find Photos where Album is CMM Challenge
b) Get Random Item from List
c) Set Wallpaper → Lock Screen
This picks a random wallpaper daily instead of sequential.
Test it
Tap Run to test. Your lockscreen should change immediately. If iOS asks permission for wallpaper changes, allow it. Done!
Pro Tip
For iOS 16.4+, you can also use the “Rotate Lock Screen” shortcut action to cycle through pre-configured Lock Screens. Create 21 Lock Screens in Settings > Wallpaper, each with a different wallpaper, and rotate through them.
Download the 21 wallpapers
Click “Download All 21” above. Save all images to a folder on your phone (e.g., CMM-Challenge/).
Option A: MacroDroid (Free — Recommended)
Install MacroDroid
Free on Google Play Store. No root required. Works on most Android phones.
Create a new Macro
Trigger: Day/Time → set to 6:00 AM daily
Action: Device Settings → Set Wallpaper → select “Next file in folder” → point to your CMM-Challenge/ folder
Constraint: None needed
Enable and test
Save the macro. Tap Test. Your wallpaper should change. MacroDroid handles sequential rotation automatically.
Option B: Tasker ($3.49 — Most Powerful)
Install Tasker
$3.49 on Play Store. The most powerful automation app for Android.
Create Profile + Task
Profile: Time → 6:00 AM, repeat every day
Task: Add action → Display → Set Wallpaper
Set Source to File, use variable %DAESSION to calculate day number, then set path: /storage/CMM-Challenge/day-%DAYNUM%.png
Option C: Samsung (Bixby Routines)
Samsung phones only
Go to Settings → Modes & Routines → Routines
If: Time = 6:00 AM daily
Then: Change wallpaper → select from gallery
Samsung's built-in wallpaper rotation can also cycle through a folder automatically.
Simplest Method
MacroDroid is the easiest for most Android users. It’s free, no root needed, and the “Next file in folder” option handles sequential Day 1 → Day 2 → Day 3 automatically. Just name your files day-01.png, day-02.png, etc.