Corrected entry: Several times during the movie they mention microwave transmitters. They use microwave bugs on people and they use microwave to synchronize the two bombs. While this is feasible, microwaves need direct visibility between transmitter and receiver, not really usable for tracking people inside buildings. Also the two bombs don't have a direct line of sight and the microwave sync would not work.
Milan Korenica
31st Jul 2019
Correction: Microwave is defined as 1ghz to 1000ghz. These ranges are routinely used for communications that penetrate buildings and other structures with windows, etc, as evidenced by their use in wireless phones, wifi, cell phones, etc.