Wireless serial port, these modules is very compact and will get the signal end to end.... They are low frequency (433mHz) and for those reasons they are very reliable in environments with lots of concrete. There is nothing more frustrating when you get your radio up and running only to find out they don't have the grunt to get the signal from end to end. This little beast really ticks all the boxes.
Voltage: 3.2 - 5.5 (lower voltage is recommended when transmitting lots of data)
Size: 27.8mm × 14.4mm × 4mm.
Frequency: 433 MHz
Factory Default: FU3, baud rate 9600bps, communication channel CH001
Line of Sight Range: 600M (ideal conditions), real world conditions 400M is probably realistic.