Alarm randomly went off and car won't start now

So this happened to me last month - Prius alarm randomly went off in the middle of the day and then I went to start the car and it didn't start. After some research I found out it probably was an issue with the 12V battery.

Bought a new 12V battery from Toyota and went ahead and replaced it. Everything was good until today.

Same thing happened about half n hour ago. Alarm randomly went off and when I went to start it the dash turned on, made some beeping sounds and then it powered off.

I only tried to start it once, because last time I kept trying and it killed the battery even faster. I'm not sure what else it can be now.

Any ideas on what could be causing this?

I replaced the 12V last month and the hybrid battery in 2020, so I'm not sure what else it could be.

Only other thing is the weather is hot here and I usually crack the windows to not let it overheat too much in the car, but then again today isn't a record hot day here.

Thanks!

 

Luckily I just found this thread - Prius won't start. No lights come on except a little lock symbol. | PriusChat

And it mentioned trying out another fob. I went ahead and tried my second fob key, inserted into the slot, and the car started no problems.

Do you think my original key fob is low on batteries and triggered a panic alarm?

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edit: I started the car a few times and it looks to be okay. Changed gears and things worked. It might be a little premature to say everything is fixed now though.

edit #2 - @JC91006 I don't have the tools to check that. I also bought the car used, so I don't know for sure if it's an aftermarket alarm. I wouldn't think so though. I've had the car for about 4 years and no problems with the alarm before. Also it sounds like a Toyota alarm.

@rjparker I'm not sure about the parastic draw. Do you need a voltmeter to check that?

 

Thankfully it got me home today with no issues after it happened. I'll see how it drives the rest of the week and give an update. Still strange the key fob had something to do with this (possibly).

 

@TMR-JWAP I haven't noticed any beeps. I do remember hearing that sound a couple years ago and finding out from here that it was because the fob battery was dying.

Drove the Prius again today and no issues with the new fob.

12V battery is new and hybrid battery is new. So if it happens again maybe it's an electrical problem, something with the alarm or a faulty 12V, but I doubt it's that.

 

Update: Sunday, June 13th

Thankfully things have been back to normal since I posted this. The alarm hasn't gone off again and the car's running beautifully. I ended up changing the fob key with a new replacement I bought a while ago.

Thanks for the advice everyone.