2006 Prius won't start but not simple dead battery

Turn on the headlights. How bright are they? If they are dim, then start by replacing the 12V battery.

If the lights are at normal brightness then the 12V battery is probably good enough to start the car.

When trying to start, make sure the brake pedal is pressed down hard. If that doesn't work, you might try disconnecting the 12V battery negative cable where it attaches to the body for a 5-minute period, thus allowing the ECUs to reset. Good luck.

 

Yep,
I find this a serious design fault for a 2007 Prius. A flat battery needs a jump start. Many will keep jumper cables in the trunk and even a small tool kit. When the Prius trunk battery goes dead it won't work the rear hatch lock. Next the choice is between contorting your self into the hatch back compartment and releasing the latch and hoping you don't get stuck when getting your jumper cables. Alternatively, you need to find someone who doesn't own a Prius and borrow their jumper cables. Then you have to open the hood and using the borrowed jumpers jumper from the fuse box. There is a substantial positive terminal but for the ground you need to use the car body.There is no need to boost charge the Prius from the other vehicle, The Prius should start right away since the Prius trunk battery is just to power the electronic switches and allow the main battery to be switched on.
Next you open the hatch back to take out your own jumper cables and then its time to start thanking the other person for not owning a Prius.
If you get the hatch back open manually you can jumper from the trunk battery itself.
Now since you can never (with a Prius ) return the favor of a jump start be sure to triple thank anyone that helps.

 

Check your 12 volt with a digital volt meter. An ok battery will be around 12.6 volt or higher. If it's signif lower, say 12.4, you'll either need a new battery or attempt to revive it with a charging session.

It's very likely due to the detailer, simply leaving a door open for an extended period (with the interior lights set to come on in such a case), and/or brushing a light switch over to permanently on position, in the course of wiping down the interior.