I am looking for something that will let me know if one of my garden gates is open or closed. I saw something in the Home Automation catalog but the magnetic switch doesn't look like it is waterproof. I have also been thinking about modifying a Craftsman Garage door open/closed system that I use but am not quite sure how to do that. Any ideas out there? Thanks JD
Virtually all of the magnetic sensors (called "contacts") used in the alarm industry are waterproof. GE Security, GRI and Honeywell all make reliable, wide-gap contacts that could easily be used for this purpose. Your choice will depend on the distance between the gate and the fence when it is closed. If it's tight fitting (less than 1/2 an inch) almost any standard door sensor will do. If the gap is larger, up to 3", you'll need one of the models used for a garage door. Standard door contacts cost between $2 and $4 and wide gap; ones for a garage door cost about $11 or so up to $27, depending on the model.
If the gate is made of iron, you'll need a wide-gap contact. These are available with brackets designed for mounting on the kind of pipe used to build fences. On a reasonably close-fitting, wooden fence gate you could fit a recessed contact which is concealed from view. If you only need one or two of the basic contacts, let me know and I'll send you a sample. I sell hundreds of door contacts from various manufacturers in my online store.
I use magnetic reed switches on outdoor gates; they are waterproof and work well BUT they can get welded by a near lightning strike. Proper protection (zeners, diodes, chokes) make them last longer. The high current ones take more abuse.