When you say "one of them does not emit a sound", I'm assuming you mean that when you press the button to test it, nothing happens??
If it's got a new battery in, firstly check the battery by putting it into another one of your smoke alarms to check it.
If the battery is okay, check the contacts on the smoke alarm. The previous battery may have corroded and be preventing the battery from making contact. A rub with some sand paper, or something like a nail file, should fix it.