2000 S4o started up without the key

[Amythewolfe]

My s40 has been up on jacks for three days( We are replacing the brakes and rotors, and ran into some bumps). Last night I looked out the window and my Volvo is running. I had the key in my hand, and the fob(which has a dying battery, it barely works). I went out to see if someone had tried to hotwire my car(which would be unnecessary considering there are only 3 wheels on it), no evidence of forced entry or start. So I put the key in the ignition and tried to shut off the car, it did not work. So I then lifted the hood and unplugged the battery, after five minutes it shut off. I have not been able to find a similar situation on the internet. I am hoping someone can help me out. I had thought maybe the previous owner set up a keyless entry, and my fob may have a button that starts the car. I have not been able to find the fob I have online to research it.

[alschnertz]

Is your key fob a factory Volvo key fob?
Does this car have an aftermarket alarm?

[abscate]

Unhooking the battery was a bad idea. Without field coil voltage your alternator was running unregulated and can fry..

Much better to find the ECU or fuel pump fuse and pull it, then disconnect battery

You certainly have an aftermarket starter or a really bad ignition switch electrical part