Lenslok is a copy protection device used to discourage software piracy.

In the 1980s, software publishers experimented with various methods to combat piracy. These included fast loaders, which made tape-to-tape copying more difficult, though often at the expense of reliability, and colour code charts that required users to reference printed materials before gameplay.

Lenslok was one of the most elaborate, and controversial, copy protection systems.

Invented by John Frost and brought to market by ASAP Developments, Lenslok combined a physical plastic device with front-end software to prevent unauthorized access to games. The idea was simple: if you didn’t own the original Lenslok device, a pirated copy of the game would be unplayable.

The Lenslok device was a small, rectangular piece of plastic containing prisms. Here's how it was used:

1. First, the game and its Lenslok protection software were loaded.
2. The user then held the Lenslok flat against the TV screen.
3. Using the keyboard, they had to resize on-screen lines to match the physical size of the device.
4. Once aligned, the device was folded into a "C" shape.
5. When held properly against the screen, the prisms would decode a scrambled image, revealing the letters OK.
6. If the letters were visible and correctly identified, a second code was displayed for the user to enter, and the game would finally start.

Lenslok had numerous flaws:

• It was overly sensitive: If the calibration was even slightly off, the system would reject the attempt and, in some cases, clear the computer's memory entirely.
• It was fragile: The plastic device was prone to breakage, especially at the ends.
• It was incompatible with small TVs: Portable TVs were a common way to play games, but Lenslok didn’t scale well to smaller screens, making the letters difficult or impossible to read.
• Every game had a different Lenslok: Devices were coded uniquely for each title and publisher. A Lenslok from Elite wouldn't work with a game from Digital Integration, for example.
• It added cost and hassle: The extra production and packaging requirements discouraged widespread adoption.

Software titles that used Lenslok were:

• Ace, Cascade
• Elite, Firebird
• Fighter Pilot, Digital Integration
• Jewels of Darkness, Level 9
• OCP Art Studio, Rainbird
• The Price of Magik, Level 9
• Silicon Dreams, Level 9
• Supercharge, Digital Precision
• Tomahawk, Digital Integration
• TT Racer Digital Integration

The device became particularly associated with Elite on the ZX Spectrum, simply due to the game’s high sales volume. The device’s unpopularity was so pronounced that when the 48K version of Elite failed to run on the new 128K Spectrum, the Lenslok system was removed from the patched version, despite not being the cause of the original issue.

Eventually, hackers and users found ways around Lenslok. One such method involved using the Multiface interface from Romantic Robot, which allowed users to modify code or save the game from memory after enduring Lenslok just once.

Lenslok came to represent a larger problem: copy protection methods that ended up inconveniencing legitimate customers more than deterring software pirates.