Yes, to test your Wi-Fi signal strength inside the house, you can use the free AirPort Utility app.
After downloading the app, go to the iPhone’s Settings, find AirPort Utility, and enable the ‘Wi-Fi Scanner’ option. You may need to close the app completely and reopen it. When you launch the app again, you’ll see a ‘Wi-Fi Scan’ button in the top-right corner.
Tap ‘Wi-Fi Scan’ to scan all available Wi-Fi networks. Under each network, you’ll see a value labeled RSSI (Received Signal Strength Indicator). This value, shown in dBm, indicates the signal strength at your current location. A value higher than -70 dBm generally means a good, usable signal.
Once you’re done, consider disabling the Wi-Fi Scanner option in Settings, as leaving it on may drain your battery faster.
There are other apps, like NetSpot WiFi Analyzer, but I haven’t tried them myself.
Hope this helps.