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

如果我们知道们频率, 我们就能听们谈话。

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

"我们一听敌方电台广播,设法查探们秘密计划。"

This instrument monitors the patient's heartbeats.

这台仪器听心跳。