Absolutely, and that sounds like a great plan there. But in the example given in the article, that 100% sounds like a recipe to get the clerk killed. The robber forces the clerk behind the counter, and then a voice says "police have been called" - surely they are going to assume the clerk did something, right? Lucky that in this case they ran away, but what if they didn't?

Like the article said - there is a reason why a silent alarm at banks is silent - it makes it safer for the employees.