If my light and the alarm noise is out, does that mean I have a low battery?

The answer above is incorrect. If the back up battery was low it says, "bat" on the screen and that's it. Since the "11" is being displayed, zone #11 on your wireless system as a low battery.

If the watch now makes no sound at all, no beeps ever, It seems like the alarm unit noise generator, has been disturbed when you opened it. Ignore the battery and look for the sound transducer behind the holes in the case where the sound comes out. Is it dirty or have any wires to it broken?

I have found the instructions on their web site but this alarm is not mentioned.

I suspect that it is a battery low indication; this would be consistent with a battery that is over a year old .

Try having the battery replaced.

Assuming that your limits are set correctly, this is a job for a Polar Authorized service center.

There is most likely a problem with the computer, depending on the age of the watch this will be taken care of under warranty. The link above explains the process.

If you replaced the battery yourself (never recommended) some contaminant could have gotten into the electronics, or the seal is no longer working allowing moisture into the unit. These are highly sensitive electronics and should only be handled through the service centers. The work they do is covered with a warranty and they replace seals and vaccuum pressure the watch to make water tight again, as well as run a diagnostic on the computer.

In the mean time if you don't want to send in you can set the Heart Rate limits - both low and high well above your actual limits and that will stop the beeping, as the beeping while you are working out is an out of limit/ zone alarm.

There should be a battery low indicator on your watch (I think).

If you haven't got instructions for your watch you can get instructions from the Timex web site "timex.com".

At the bottom of the screen click on "manuals/downloads", then on "product
manual download"

Enter your watch type in the search box and click on "search"

There should be mention of a battery monitor if there is one.

Turn the alarm off two times. If it still indicates A/C not ready, press the * key and it will tell you what zone is open or what zone has a low battery.

If your model is not an automatic movement then it means your battery is too low in remaining power to support the watch.

No, there is nothing wrong with the alarm in your watch.
The sound in all watches are generated by passing vibrations to the metal tweeter which is connected to the watch caseback inside the watch. As the surface of the watch is quite small, there is not efficient power to spred the vibrations over the caseback surface, hence low volume of the alarm. No wristwatch in the world is capable of loud alarm sound yet. This is something the scientists have to work with.
The plastic protector is definetly affecting the volume. Take it off and you will notice slightly better sound. This protector actually is ment to protect watch caseback from scratches prior to selling it to the customer and have no use after that. In fact it only collects the dirt and bacteria and can affect your skin as the caseback as well.
Another sound improvement can be the new battery if the original is underpowered. Alarm feature uses the most of the energy stored in battery and the power consumption is higher than all watch movement parts put together.

Rate me, please.

You probably lost SPRING COIL while changing battery. It connects movement to sound membrane. See watchmaker to sort this.

The "eye" icon appears when you have your backlight set to auto. that means when you move your wrist to look at your watch the light comes on automatically. I have found this to be a huge drain on the life of the battery. to turn it off hold down the light button (the grey button on the front with the red "g" on it) untill you hear it beep.

As for the watch dieing when the alarm goes off that is a good indication that you need a new battery.