Can one FOB used on two different systems?

As the tillte says, can I used one FOB on two different systems? Thanks.

Are you referring to an RF Keyfob like the KEY2-345? If so, yes. The standard RF sensors and keyfobs are not themselves limited to a single panel and can be learned into additional compatible panels.

The two systems should not be physically close enough that a keyfob may be able to reach both at the same time. (for example, an outbuilding with its own system located within RF range)

Yes, a KEY2-345. The systems are about 50 miles apart. This will work great for my parents. Thanks again.