How to read signal strength of all frequencies received by antennae

Since all smart phones have antennas, and these antennas are capable of detecting and receiving many types of signals including wifi, 2g, 3g, 4g, and 5g, then "we" should be able to make apps that help us observe the strength and presense of all these signals independent of the SIM card we happen to have and whether or not our phone is in airplane mode, correct? However, the signal-detector type Android apps I see out there only work when the radio transmitter is powered on, and even then it's limited to the particular service addressed to our SiM. Am I missing some vital factoid? I feel I must be. Something is not adding up for me. I do have a dedicated EMF detector "Electro-smog Meter". It doesn't have transmitters yet it's antennae seem to work just fine.