An audible signal that would indicate the valve's opening and closing had been disabled.
As far as I could tell, the child hadn't made a sound, but it may have emitted a signal audible only to its mother.
What woke him was an audible signal that he was wanted.
The actual size of the target can be calculated using the audible signal.
The beginning of every period and, usually, break is announced with an audible signal such as a bell.
In such instances, an audible signal would sound and play was suspended at that point.
With real low bass, speakers have to work very hard to produce enough of the relevant frequency to make the signal audible.
I therefore wonder again whether it is necessary to introduce a requirement for an audible signal when this happens.
Lights may be appropriate, but audible signals are perhaps a bit doubtful.
A long serve is indicated by an audible signal.