Davdi
Android Expert
Regarding the 'Numbers Station' Gong/chimes: I believe that numbers stations are generally used by various countrie's 'security/Intelligence (i.e.spy) services to send coded messages to their agents.
I got this of a TV Documentary, so can't vouch for the accuracy.
However, Wikipedia says at https://en.wikipedia.org/wiki/Numbers_station :
A numbers station is a shortwave radio station characterized by broadcasts of formatted numbers, which are believed to be addressed to intelligence officers operating in foreign countries.[1] Most identified stations use speech synthesis to vocalize numbers, although digital modes such as phase-shift keying and frequency-shift keying, as well as Morse code transmissions, are not uncommon. Most stations have set time schedules, or schedule patterns; however, other stations appear to broadcast at random times. Stations may or may not have set frequencies in the HF band.[2]
I got this of a TV Documentary, so can't vouch for the accuracy.
However, Wikipedia says at https://en.wikipedia.org/wiki/Numbers_station :
A numbers station is a shortwave radio station characterized by broadcasts of formatted numbers, which are believed to be addressed to intelligence officers operating in foreign countries.[1] Most identified stations use speech synthesis to vocalize numbers, although digital modes such as phase-shift keying and frequency-shift keying, as well as Morse code transmissions, are not uncommon. Most stations have set time schedules, or schedule patterns; however, other stations appear to broadcast at random times. Stations may or may not have set frequencies in the HF band.[2]