Number of numbers
Slightly OT, but this got me thinking about the PIN that I can set to secure my smartphone. There are a few different security mechanisms (pattern, fingerprint, etc.) as well, but I'm just thinking about the PIN option here.
The phone allows me to select a PIN of my choice, of 4 (no more, no fewer*) digits. A couple of decades ago I had a Nokia brick-ette which allowed me to set a PIN of more than 4 digits (for whatever reason, I settled on a 5-digit PIN which by reckoning is 10 times more secure than what my modern smartphone supports. Even if you know the digits involved, it's a case of 24 versus 120 different combinations.
* I know that wording jars, but it's grammatically correct