The FDIC only has about $25 Billion in deposit insurance fund, and by law they can keep a balance of only slightly above 1% of all deposits. The banks cannot afford a cash run, and the Feds know it.
If you try to take more than $3,000 from any bank in cash tomorrow, I can almost guarantee you that your name and account will be forwarded to the IRS, DEA, and FBI. Even though Federal law dictates the make amount to "alert interest" is $10K, banks report at a much, much lower threshold, and have for years.
You can pull out some cash and start using it.
The Patriot Act lowered the Threshold from $10k to $3k.
I believe you are talking about “unusual account activity”.