Head units aren’t always-on. Typically they go into a low power standby 2-5 minutes after ignition / accessory mode turns off, and go completely power-off 30-ish minutes later.

Otherwise any car sitting unused for a week or two would have a dead battery.

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Zigurd 5 hours ago | parent | next [-]

I learned that not all electronics goes into low power mode even when designed to run off a car battery, from using a cheap Bluetooth OBDII dongle.

	▲	smilespray 4 hours ago \| parent [-]
		If that was one of those ELM327 dongles, yes they have 12V and are known to drain your battery. They're only meant for short diagnostic runs.

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olyjohn 5 hours ago | parent | prev | next [-]

They are always wired to battery power though. The point is that it could look powered off, and still be running a proxy.

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lmz 2 hours ago | parent [-]

You would hope that the ignition switch really cuts the power to the head unit when it is switched to off.

	▲	carstenhag 2 hours ago \| parent [-]
		No you wouldn’t, because then you always have a cold boot of the headunit, even if you just accidentally hit the ignition. Users want the head unit to resume within a few seconds. Just like their phone.

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kotaKat 4 hours ago | parent | prev [-]

Some of these Android units also double as DVRs and dashcam recorders (parking mode!) as well so may be hooked onto the normal +12v rail.