I have a small device that has a 3.5 mm jack for the serial connection. The protocol is uses is known so I don't have to worry about figuring that out. What I am having trouble with is figuring out how to physically hook it up.
Is it as simple as:
Device TX ---> Arduino RX Device RX ---> Arduino TX
The device runs on a small coin cell battery so am almost sure the voltage levels will be the same.