The logic gates are a connectable agent included with Creatures 3. They are all gadgets. The logic gates allow you to use Boolean logic to create your connectable agent setups. The AND gate is shaped like a semi-circle, and the OR gate is shaped like a crescent moon. They can be used in a DS-standalone world by downloading the DS Connective Agent Pack.
The AND gate will take two inputs and produce one output. It will only send an output if it receives two signals.
The OR gate will send an output with the strength of 255 if either of the two inputs gets a signal. Note that this means that both inputs do not need to be connected for the OR gate to work. OR gates are particularly useful to devise setups like 'when the lift button is activated OR the contact sensor detects a creature, then activate something else' (like the Cheese Machine or an Anti-Bacterial Spray).
The NOT gate will send an output with the strength of 255 if it does not get any inputs. If it does get an input, it stops its output.