BestBuy regularly runs a "free install" with remote start systems I paid just under 300 out the door Over Christmas they had the compustar 4202s its a 2 way system. You do not have to sacrifice a key. I went in with 1 key and left with that same key

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I assume it works by using a fake chip programed into the system so it thinks there is a key in the ignition. I say this because if you use the remote start it locks out other remotes from unlocking the door. You have to use the remote starter fob or the key in the lock to open a door. If you don't use the remote start you can use your regular remote to lock or unlock.
If you have the remote start running when you get in you simply put the key in turn it 2 clicks < not all the way to engage the starter> and when you touch the brake peddle it turns control over to the key in the ignition. If you want to leave the car running when you get somewhere after you put the car in park while the car is running hit the remote start button then you can take the key out and it will keep running unless you tap the brake peddle then it kills it. That is how it stops someone from stealing your remote started car
My 2014 Challenger R/T has remote start and after having it I cant live without it lol. Nothing like a nice warm car with clear glass in 30 Deg weather. My 2000 Land Cruiser lives outside.
I will say be ready for a long install. My guy had issues with his programing cable He said it was 14 years old and gave up the ghost after working on it for a long while he grabbed a cable from one of the alarms and the shelf and it happened to have a cable with the same connectors on it. I was quoted 4 hours and it took 6.5 hours all said and done.