If we can know their frequency we will monitor their talking.

如果知道的频率, 就能监听的谈。

We have been monitoring the enemy's radio broadcasts to try to find out their secret plans.

"一直在监听敌方的电台广播,设法查探的秘密计划。"

This instrument monitors the patient's heartbeats.

这台仪器监听病人的心。