Pin 16 on your OBD port will have power regardless of the position your ignition is in. It's always hot, delivering battery voltage and allowing up to 4 amps draw. Pins 4 and 5 are ground.
Whether your satnav will draw current if turned off depends on your satnav. Some satnavs will recharge their internal battery if plugged into a power source, even if turned off.
To be safe I would unplug your satnav when you turn the engine off and only plug it in if the engine is on.
Or you could be like me and get a deep discharge battery for your car. Then it's safe (or at least, safer) to run your electronics off the battery even if the engine is off. A regular car battery can be drained by electronics more quickly than you might think so it won't be able to start your car.