Your lock is the defense that does not need gear. Player guides tell you to step on the yellow circle inside the base. They describe 60 seconds for a new player. The rebirth table then adds 10 seconds on every row, including rebirth 1.
The lock ends on its own. Lock again before you go hunting. A base you left open is a base other players are told to enter.
Floors
Rebirth 2 builds the second floor and rebirth 10 builds the third. The rebirth article says a brainrot on a higher floor is harder to steal. Put the unit you are saving for a later requirement, or your best income unit, up there. Leave replaceable units on the ground floor if you need the slot.
Gear that answers a thief
All Seeing Sentry from rebirth 7 shoots players who get close. Traps show up in almost every public steal combo, so a trap of your own on the path back to your base is the mirror of those combos. Subspace Mine arrives with rebirth 14. An August 2025 update note prices a Subspace Mine at $500M and a Gummy Slap at $400M. The rebirth table calls the rebirth 14 slap a Gummy Bear. Check the shop name before you buy.
Body Swap and Invisibility Cloak are attacker tools from rebirths 10 and 4. If you own them, they also get you home. They do not replace the lock.
While you rebirth
Most of your cash drops. Required brainrots are consumed. Other brainrots stay only if they are already placed and are not the named requirement. Anything still walking home returns to the carpet, where the whole server can buy it. Finish the walk, then rebirth.