Magnetic nano

They often have an O-ring seal between the lid and the body to make them easier to open and partially waterproof.

Magnetic nanos were originally manufactured in 2001 to store flashing LED lights for use as jewellery, giving them the colloquial name 'blinkies'.

[2] When it was discovered that magnetic nanos can be used as geocache containers, they were quickly mass-produced and sold for that purpose.

[4][5] Due to their very small size, they have become especially popular in urban locations (particularly cities), allowing for geocaches to easily be hidden in these areas.

[9][4] Also, in cold conditions, if no rubber seal is present, then the nano can freeze and become difficult to open.