PE whistle with restricted sound carrying so ideal for pitches surrounded by houses
Can be used in any circumstance where you don't need the sound to carry long distances.
We have had these tested with London Underground as useful on platforms.
Based upon the standard Thunderer 622 plastic whistle with a restricter in the mouthpiece
This is commonly called the MUGA whistle (Multi Use Game Area)

Note - as a restricted whistle, the more you blow it will not get any louder. It is also not as loud as a normal whistle which may take some getting used to.