How do I replace the battery in a Bowflex wr30m monitor?

Maybe the battery doesn't have enough power for the sounder.

Easiest way is to take watch to a watch repair, jewelry store, or big box store like Walmart. They can sell you that battery and install it for you.
To determine the battery type, you will need to refer to your manual, or you can try looking on the back of your watch (which sometimes lists the battery type.)

click this link below for instruction manual
http://www.timex.ca/library/misc/7d8a360a-3d84-4326-91e2-3c2ae3bc2d6d.pdf

In time mode, hold set (bottom right button) to change date and time. The selected (flashing) item can be changed in one direction only using the up (top right) button. Press set again to cycle through each item until desired settings are chosen.
In stop watch mode, the up button starts and stops the stopwatch, the set button will take a split time while the time is running. To reset the stopwatch, press set once while the time is stopped.
In alarm mode, the up button turns the alarm on and off. There are three alarms available. To cycle though alarm times, press set. To set an alarm, press and hold set until the time flashes, then set the alarm time using the up button, cycle through hour and minutes using the set button. When finished, press set again.
Timer mode. To set the timer time, press and hold set until the time flashes. The timer goes up to 23h:59m:00s. You cannot set seconds. Once set, the timer can be started and stopped using the up button. There is no reset for the timer, to start a new timer the time must be manual changed again.
To check heart rate, press and hold mode until PUL is shown, place two fingers, one each on the top and bottom metal contacts for 6-10 seconds to get reading (This works best when not in motion).

Should have been a CR2016 THAT'S PROBABLY WHY ITS NOT WORKING YOU HAVE THE WRONG BATTERY IN IT!

Try this:
search-manual-online.com/bowflex-precision-xt-heart-rate...

Try a very small dab of a very light lubrican on the sealing edges.

If you haven't already tried it, press the edge of the watch back using two fingers and move them appart until they meet again.

Season with a lot of parience... good luck!

HOW TO REPLACE BATTERY IN MY POLAR TARGET WITH A TS1 TRANSMITTER

Yes, you definetely need battery replacement.
As the hart rate monitoring is most sophisticated part of the device, it has more IC (Integrated Circuits) than any other features.
More IC's means more power is needed, so, if the heart rate monitor is starting to malfunction, that's the very first sign of underpowered battery.
Find your nearest watch repair shop and ask for battery replacement.

Do not forget to rate, please.