pinger versus transponder
I would be extremely skeptical of the Chinese operatng their hand held Teledyne detector receiver. The avionics acoustic pinger that is currently used has not changed much in the last 50 years and although it can supposedly operate for 30 days, I doubt whether it can be detected outside a 500m range. Diver's bells also use this safety equipment in the form a transponder on the same 37.5Khz freq which will give a range and bearing which a pinger will not do, when interrogated but with more range but I have never seen one operate in ideal conditions beyond 600m.