Using a whistle for training
A whistle carries no built-in meaning to a dog - it becomes a command through pairing. Pick one pattern per behavior (one long blast = come, two short = sit), play it, cue the behavior the dog already knows, reward immediately, and repeat over short daily sessions. The whistle's advantages over voice: it cuts through distance and wind, it never sounds angry or excited, and it is identical every time.
Keep bursts under a second or two, at moderate volume, with the device pointed away from the dog's ears. Dogs hear these frequencies much more intensely than we do - the goal is attention, not discomfort.
The honest limits of an online whistle
Dogs hear up to roughly 45-65 kHz; physical dog whistles operate at 23-54 kHz. Phone and laptop speakers cannot reach that - their output collapses above about 20-22 kHz, and this tool honestly stops at 22 kHz rather than pretending otherwise. In the 16-22 kHz band an online whistle still does the job at close range: the dog hears a clear tone, most adults hear nothing.
For long-distance field work (hunting, herding recall at 200 m), buy a physical whistle - it is louder and higher than any speaker. For indoor training, attention cues, and experimenting before you commit to one, this page is enough. Test what you can hear yourself with the mosquito tone or the full hearing test.