Clearly, rather than just trying to remember, I had to find an unnecessarily complex and technology-oriented solution.
Even if you aren't as much of a scatterbrain as I am, car theft is a problem. Alarms are universally annoying and universally ignored. On Star and Low Jack are expensive. How do you avoid coming out to your parking space to find a bit of broken glass and nothing else? Make starting it a complex and arcane ritual beyond the comprehension of the uninitiated.