Sure, I’d like to help you and save your gear from destruction by selling you my line-of-sight roof reminders, BUT you could do this for “free” with your own phone without a hang tag. Cross your fingers your phone works every time, and the volume is up or not silenced for some reason. Also, if you don’t have a location reminder set for every drive-through, car wash, or low underpass etc. you may want to think about only relying on an app. Nevertheless, below are options for alternatives or additional backup for the hang tags for iOS and Android.
Roof Rack Reminder for iPhones
iPhones come with an app that you may or may not use called “Reminders.” I created an infographic below to help you with the Reminder app. I hope you find this helpful, and consider kicking down a donation for this information should you opt for no hang tag.
I don’t have any infographics for Androids, but there are apps available similar to the ones described above: https://play.google.com/store/search?q=location%20alerts&c=apps