IMPORTANT: future support by ANDROID OS (9,10+) can be disabled - you are buying this app for your current tested version of Android OS

https://developer.android.com/reference/android/net/wifi/WifiManager.html#startScan()
"This method was deprecated in API level 28. The ability for apps to trigger scan requests will be removed in a future release. "

Android PIE 9 - 4 scans per 2 minutes probably
Android Q 10 - probably without any wifi scan support

Wifi Heat Map let you create heat map of wifi signal quality in your flat, house, apartment or shop. Just draw your flat on the paper or use existing plans, take a picture by device camera. After that just walk in desired space and click on display on your exact location. Signal quality of your wifi will be placed on that map.

!!! Important NOTE:
As announced on Google's blog ( https://android-developers.googleblog.com/2017/12/improving-app-security-and-performance.html ) all apps which will be updated on Google Play will have to switch to current Android SDK (software development kit). Apps with older SDK with no run-time permission model will not be able to publish updates.

Because of this all apps (this also) will eventually require LOCATION permission as noted here:
official website android.com: http://developer.android.com/about/versions/marshmallow/android-6.0-changes.html#behavior-hardware-id

"To access the hardware identifiers of nearby external devices via Bluetooth and Wi-Fi scans, your app must now have the ACCESS_FINE_LOCATION or ACCESS_COARSE_LOCATION permissions:"