Will a OBD2 HUD drain battery if left?

[DSykes]

Seen a nice aftermarket HUD unit that plugs into the obd2 port and displays info.

Can this device draw power even when the ignition is off?

My car sometimes sits for a few days without use so I wouldn't want to damage the battery.

Thanks.

[Davo456gt]

my chinese £10 one switched off when the engine stopped, so no drain at all.

Think I might have it around somewhere..