Inside view of a roller garage door
In most basic models of roller shutter garage doors there is little or no security at all and they can actually be quite easily lifted up from the bottom. As most roller garage doors are electrically operated in the UK, the electric motor simply lifts and lowers the door curtain and relies entirely on gravity for the operation. When fully closed, the roller curtain is simply hanging from the barrel inside. Although many models will state there are various security 'straps' attaching the curtain to the barrel and performing some kind of security function, the reality is they are either totally ineffective or easily pushed back against or broken.
When a curtain is held from the barrel using thick, extruded and very strong solid attachments along the width of the curtain then the motor in the barrel will hold the curtain down far more effectively. The same applies for certain models where the curtain is fixed directly to the barrel, but this doesn't make for a very effective closing position on the door and can leave larger gaps at the top behind the lintel. A full hood cover will assist in preventing a roller door curtain being lifted as well.
A few roller door models have other mechanical locking methods such as a steel bar in the top section of the curtain. This sits neatly underneath a solid block either side when closed making the curtain impossible to lift, and this is about as good as you can expect from a domestic electric roller shutter door. Patented and special side guides also offer an anti-lift feature and these are in a couple of models available in the UK.
It is possible to fit various manual locks to an electric roller garage door, so if you wanted to lock down the door when closed you could either lock the bottom slat to the floor with a ground lock or insert 'bullet' lock pins into the guides either side to hold the curtain at mid height. However, if you do this then isolating the electric motor drive would be a fairly essential action to prevent accidental operation of the motor whilst the locks are in place, so this method is perhaps only ever suitable when people intend to not use the door for longer periods of time.
Of course, other factors, including the actual strength of the curtain lath sections used in the door construction affect overall security. Some very lightweight slats used in lower specification roller doors are often way too easy to bend and break and would also be fairly easy to cut through without a lot of noise or effort.
The slats used in various electric roller garage doors vary a lot more than might be assumed from their initial visual appearance. You will basically get what you pay for in this area of the door.
Most people looking at roller garage doors in the UK will find themselves discussing 'double skinned insulated' doors using a twin wall aluminium curtain, but the stronger door curtains for security are mainly single skin slat sections with a construction specifically designed for security so do not dismiss this type of door and certainly do not overestimate the levels of insulation provided as it is often minimal unless you go for a door with an actual tested and certified insulation value.
A certified security roller garage door with LPS1175 level 2 (SR2) or higher will usually be a single skin construction, so if you are really serious about security this is what you will be looking at.
The side guides used also play a bit part in overall security usually with larger width guides providing more lateral strength and resistance to force. Reinforced guides can often be specified too with additional steel section enhancements in the bottom section where they are most vulnerable to attack with tools.
Check the guide size and make sure it is at least 60mm wide as a minimum either side of the curtain, preferably 75 or 90mm wide. Some manufacturers are 110mm but this doesn't necessarily mean the curtain is actually sitting in the guide any more than a 90mm guide.
So what about the electric motor using radio controls? How secure is this? Some roller doors use coded technology with the remote control handsets and other access controls providing encrypted signals to operate the door, This means it is almost impossible to copy the signal of the door and the only vulnerable radio controls will be very basic low priced transmitters using older technology. Cheap transmitters can often have very few variable in their coding so could easily be copied with some minimal effort. There is however no great evidence of code grabbing being a problem in the UK at present but it is nice to have reliable remote handsets whatever the security levels. Remote handsets which don't work very well are a complete pain for the user.
Any electric roller garage door should always have a manual emergency override system as standard and this is normally situated inside the garage in case of a power failure or other issue.
However it is possible to make the override inaccessible to anyone by incorporating a lockable cover plate for example making the security better and reduce the chance of someone manually operating the door for access.
Manual Roller Doors
Of course we haven't mentioned manual roller doors yet and there are plenty of options here for single width garage openings. A spring balanced single width manual roller door generally uses a centrally positioned handle with a key lock which will push two locking rods sideways onto the side guides. Reasonable effective in most standard forms but there are different levels of quality and therefore security in these types of doors. Again, additional locks can be added to the bottom or the side guides in a different position.
Considering the single biggest question asked for almost any type of garage door is 'How secure is it?' the answer is never straightforward itself. The overall construction and quality of the roller door will usually determine the level of basic security and if you want tested security products then the discussion is far more involved. The only conclusion however is that a low quality low priced roller garage door will usually not be secure at all, which is perhaps more obvious than it seems. The best thing to do if security is of concern is some proper research and try to see some examples in a showroom or example nearby installation to you but make sure you understand exactly how the door secures before making your decisions.
Also, see various information pages on higher specification roller garage doors.