The fact that Apple will not open WiFi Scanning to 3rd party apps means there seems to be nothing on the App Store that can do this job and most people resort to walking around their house (or wherever they need to scan) with a laptop in their arms, not the most convenient option.
However, there is a simple solution using a native Apple iPhone app which few iPhone users are aware of. WiFi scanning on the iPhone can be done using the AirPort Utility app.
The first step is to download the AirPort Utility app from the App Store, it’s free of charge so the price is right! Once the app is downloaded to your iPhone select settings (the small grey icon with circles on it) and scroll down to the setting for the AirPort Utility app and select it. The screen below (img.1) will be visible, as shown on the screen shot turn the WiFi Scanner option on.
When this is done go to the AirPort Utility app and tap on it to load it in. The screen below will be displayed (img.2) with the option at the top to WiFi Scan. Now tap the WiFi Scan option.
The screen below will then be shown (img.3). If you are scanning around the house for signal strength, noise, channels, etc. it’s probably best to keep the scan on Continuous. Then just tap scan.
This will then scan for information about WiFi networks that are within range and will be displayed as below (img.4).
Once you have obtained the information required you can then return to AirPort Utility settings to switch off the WiFi Scanner option in order to maintain battery life.
The above steps give you access to a free convenient WiFi Scanner.