While Nothing doesn't have a native *#*#4636#*#* (Testing menu) like stock Android, you can try it. Note: On Nothing OS 2.5, *#*#4636#*#* partially works—it shows "Phone Information," "Battery History," and "Usage Statistics." You can see your exact battery temperature (in Celsius) and signal strength in dBm, which is better than the misleading icon bar.

This is arguably the most useful code for any Android power user. When dialed on the NOTHING Phone (1), it opens a menu titled with four distinct options: