Puzzles: Jigsaws, word finds, word jumbles, crosswords, etc.

First appearance: 19th century.

Security: Varies.

Reward: Low. If everyone gets the same puzzle, the reward for solving it can’t be anything too valuable. At best, maybe a coupon in jigsaw form.

Secret Decoder Rings (here, as available for purchase on ThinkGeek)

First appearance: Depression Era.

Security: Medium.

Reward: Low. Secret message is likely to be a simple advertisement for, say, Ovaltine.

Secret Game Pieces

First appearance: 1960s.

Security: High.

Reward: High—potentially millions of dollars. May require the collection of several pieces.

Red Plastic Secret Decoder

First appearance: 1970s.

Security: Laughably low.

Reward: Varies, depending on whether or not the game pieces are unique. If so, potentially high. If not, reward is likely to be nil.

Magic Eye Pictures

First appearance: 1980s.

Security: For some, low. For others, impossibly high.

Reward: Low. It’s usually just a stupid photo of a duck or something.

Secret Web Codes

First appearance: 1990s.

Security: High.

Reward: Potentially high, if you actually want to save your dirty Blizzard cup, bring it home, go to the website, create an account, and enter the code. Evidence suggests that fewer than ten secret web codes have ever actually been redeemed.

QR Codes

First appearance: 2000s.

Security: High.

Reward: Usually an app—either an appetizer or an application.

– Jay Gabler