Just saw this thread and oh man, I literally went through this exact same thing last year!! I was so nervous about messing up my 2005 Impala's security system but I reallyyy wanted to avoid that freezing walk to the car in January lol. I'm still kinda new to doing my own car stuff, but I basically spent weeks researching.

I ended up going with the Compustar CS4900-S All-in-One Remote Start and Keyless Entry System and honestly, it was such a journey! I also had to get the iDatalink ADS-ALCA Multi-Platform Bypass Module cuz that Pass-Lock system is no joke. Seriously, if you dont get the bypass module flashed right, the car just won't crank.

1. It was lowkey terrifying seeing all those wires at first!!
2. I found out the Viper 4115V 1-Way Remote Start System is another solid budget option too.
3. Making sure the ground wire was tight basically solved my first failed attempt haha.

Idk if that helps, but it feels sooo good when it finally clicks and starts from the kitchen window! Good luck!!

Sooo, I actually did this exact project on my old 2004 Impala a couple winters back. Dealing with that GM Pass-Lock system is honestly the biggest hurdle because if you dont bypass it right, the car just wont start or the security light stays on forever.

In my experience, I would suggest going with a Compustar system paired with a dedicated bypass module. It’s basically what I used, and it worked flawlessly even in sub-zero temps.

WARNING: Avoid the super cheap "universal" kits you see on auction sites. They usually lack the specific data instructions for the Pass-Lock II or III sensors, and you'll end up hacking your wiring harness which is a total nightmare.

Here's what I recommend based on my install:
- Get a blade-style bypass module; it slides right into the main brain.
- Look for a T-harness if you can find one, it makes it way more plug-and-play.
- Stick with Viper or Compustar cuz their technical manuals are actually readable.

It works great once you get the timing on the tach-learning phase down. Good luck!

Story time: I actually tried going the cheap DIY route on my old Chevy back in the day and literally spent a whole weekend fighting with the Pass-lock wiring... honestly, it's kinda tricky if you're trying to keep the budget low. Quick question tho, are you planning to install this yourself or take it to a shop? Also, are you looking for a basic one-button remote or do you need a two-way pager?

Seconding the recommendation above! Honestly, safety is huge so don't cheap out on the bypass. I'd look at Directed Electronics Inc 556UW Universal Immobilizer Bypass since it's like $30 and reliable for budget builds.