I opened the siren with a hacksaw, this is what I found.. Can I fix this?

 

Forgot to upload photo, here it is..

 

Only if you can work miracles.

 

I would say, maybe? If you replace those batteries, clean up the pc board and any damaged traces (and it works), you'll have saved some $. Cost of replacement batteries (if bad) is pretty inexpensive but even the new available replacement batteries need a slight modification. If I opened up a siren like this, I would shelve it for a rainy-day project. A replacement siren depends on where you get it, and if it has dead rechargables inside it as well you'll still have to replace them. A new one may have been in storage for many years (again, battery viability), so even that could be an issue with getting one that has good batteries in it. If there is no other damage to the siren, and you can acquire these ( http://www.ebay.com/itm/2Pcs-Ni-MH-Button-Rechargeable-Battery-3-6V-150MAH-PLC-Data-backup-power-2P-1P-/221023510118?pt=LH_DefaultDomain_0&hash=item3376071e66 ) and mount them correctly (both sides in the 4 contact points, the neg side single pin to a double pin), then it might have a new lease on life again. There is a great .pdf somewhere here to repair the siren (with the battery mod detailed). Good luck!




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That one is pretty much toast.
I've been into 5 of them so far, 3 were like that, not worth the effort.
I was successful with the other 2.