I have a key lock box discretely attached to my car
ShurLok SL-600W 4 Dial Numbered Key Storage Combination Lock Box, Blue https://www.amazon.com/dp/B00HR01VJA/ref=cm_sw_r_cp_api_iFs-xbFDJCHS8
If I get locked out, just need to know the combination to get to the spare key for my car. Also keep a spare house key hidden in my trunk. If I'm locked out of my car or my house (or both) I have a way to remedy the situation.
The important thing to remember is that you need to make sure you purchase a lock box that is big enough for your car key.
Clever arrangement, but a certain point, lockboxes become the more economical option.
Or https://www.amazon.com/dp/B00HR01VJA/ Attach to some solid body element.
...they're only like $15 on amazon