A mechanical mod is a device which holds a battery, has a switch with mechanical parts which when pressed moves a conductive contact to meet the negative contact of the battery, completing the circuit. The positive pole of the battery touches a contact which transfers power to the atomiser. There is no short circuit protection, no battery management and no power regulation, unless the user opts to install a small device called a Kick, which transforms the mech into a regulated VW device. The user could instead install a safety fuse, which would offer battery protection.
The mech mod typically has very little voltage drop, and delivers a far superior vape to most regulated mods. The user has to be very mindful of not over discharging their battery, which would be dangerous. The user also has to be very mindful of the electrical resistance of their atomiser, and use Ohms law to ensure that they don't exceed the maximum sustained current rating of their battery
Mech mods come in all shapes and sizes, but mostly mech mods are very much more beautiful than regulated mods