Aftermarket parking sensor install?

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14' Mazda6 GT Tech, 17' Kia Sorento SXL V6 AWD V6, BMW S1000R/RR
Has anyone installed aftermarket sensors (found for $20 over amazon/ebay/aliexpress)? Are there marked spots inside the bumper where to drill. I will make a DIY as I am planning to install.
 
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2017 Mazda CX-5 GT, 2016 Mazda6 iGT, 2014 Mazda3 sGT hatchback
I did that for 3 vehicles I used to own.
No marking or instruction that came with these cheaper products.
You basically get a box, a beeper, few sensors with connectors, and maybe a drill bit.
You tie the power to the backup light.

Cheaper products tend to develop false alarms more frequently, especially in rains.
 
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14' Mazda6 GT Tech, 17' Kia Sorento SXL V6 AWD V6, BMW S1000R/RR
I have done it before on my Nissan Rogue which already had markings inside the bumper. Wondering if mazda has those since it’s an option.
 
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