Can an Apple Watch be used to notify help in case the wearer falls?

Yes. See: Use fall detection with Apple Watch - Apple Support

Texasge wrote:

Can an Apple Watch be used to alert help if the wearer falls and can’t get up?

As mentioned, yes.

Wrinkle to consider: Some of the cases where this automatic fall detection might be useful can involve folks that aren’t necessarily good at keeping an Apple Watch charged, or at wearing the watch consistently. For those that can and do, it works well.

Series 5 battery life is ~two days, locally.

Another alternative because not all watches have fall detection;

Use Emergency SOS on your Apple Watch - Apple Support