Kops Make Great Theft Prevention Experts is a mnemonic for prefixes from SI units. The theme of this mnemonic is NetHack.
An SI unit, such as a metre, gram, litre, or newton, can have a prefix attached to represent a power of ten, such as 1,000. For example, a kilometre (km) is 1,000 metres, a megagram (Mg) is 1,000,000 grams, a gigalitre (GL) is 1,000,000,000 litres. This has applications in computing also: a kilobyte is varingly 1,000 or 1,024 bytes. (The number 1,024 is 2 to the 10th power; a megabyte would have 2 to the 20th power bytes.)
The mnemonic Kops Make Great Theft Prevention Experts is to memorise the order of of prefixes for every third power of ten from 3 to 18:
| kilo- | Mega- | Giga- | Tera- | Peta- | Exa- |
| 103 | 106 | 109 | 1012 | 1015 | 1018 |
The abbreviated prefix (for example, km for kilometer, MB for megabyte) is always uppercase, except that k for kilo- is lowercase. The mnemonic does not help here; Kops is the only proper noun.
The mnemonic is also flawed. During actual gameplay, Keystone Kops do not appear until after you rob a shop. Thus they do not actually prevent the theft, they react to it! The shopkeeper, by blocking the door, is actually the best theft prevention expert.