Unbreakable glass windows are made by many companies that claim to have the strongest glass panes. The strength is determined by the amount of force used to break or shatter the glass. When replacing your windows with unbreakable glass you will simply remove the old windows and install the new ones. In most every case they will have to be custom built to your window dimensions. All you have to do is measure your window length and width (from inside the jambs) and then give the dimensions to a custom unbreakable glass window manufacturer. The windows install just like any other.
Cost is something to consider when replacing the windows. Some unbreakable glass is much more expensive than traditional glass windows. This is because of the process used to manufacture the glass and make it a stronger product. Some of this process involves heat tempering or chemical washes that increase the strength of the glass. Another consideration is heat efficiency. Unbreakable glass may be stronger, but if it is not double paned, it will not be as heat efficient. The savings you incur by never having to replace a broken window might just fly right out that window with lost heat.
There is no doubt that replacing your home windows with unbreakable glass is best done by a professional. A professional installation can ensure that the new windows provide the highest heat efficiency possible by leaving no gaps or drafts. They will also be able to help you select the right kind of unbreakable glass. If safety is your main concern, the addition of new unbreakable glass windows is an excellent idea. Just be sure you check the "unbreakable" strength ratings of the glass and consider all the other options before replacing your windows. You can always install shatterproof film to make any window unbreakable as another option.