The 900 MHz Radio Shack (model 43-3102, FCC ID
AAO4303102) intercoms are useful with several hundred feet range with the 1mW RF output and wideband (75kHz) FM modulation, specified at -109 dBm 20 dB SINAD sensitivity (very good).
However, the squelch is set a bit too tight in my opinion from the factory. Since they use a CTCSS system using several of the same frequencies as standard two-way radios, it is possible to “loosen” the squelch (allowing weaker RF signals to be heard) without falsely opening the squelch on static.
The squelch potentiometer makes the squelch “tighter” with counterclockwise turning and “looser” with clockwise turning. When the squelch is open (but with no/incorrect CTCSS) the middle RX LED will flicker once per second. When the squelch is set just tight enough to stop the RX LED from flashing with no incoming RF signal, the RF RX sensitivity is maximum (maximum range).