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I purchased this pool door alarm (289-4,) along with a reentry button (084-3).

My house came pre-wired with magnetic door and window contacts (normally closed I believe.)

I do not have a home alarm installed at this time. My plan is to pickup the wires from the reed switches I want monitored by the pool door alarm and run them back to the pool alarm.

I think I am good up until this point.

Next, If I ever want to install a home alarm in the future, could I share those reed switches between the pool door alarm and the home alarm? I thought yes, but someone told me no recently. I figured the alarms are just checking for continuity. Can that not be done at the same time by two different alarm systems?

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I figured the alarms are just checking for continuity. Can that not be done at the same time by two different alarm systems?

No, that is generally not the case.

Besides which, do you really want a fault in one system to affect the other?

Either use two switches on the door, or use a small DPST relay controlled by the switch to multiply the number of independent contacts avaiable.

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  • \$\begingroup\$ Thanks! So what type of relay would I use or how would that be wired up? My understanding is relays typically use a small input voltage to open the contacts on a NC relay or a small amount of input voltage to close the contacts on a NO relay... How would magnetic door contacts fit into that? \$\endgroup\$
    – Talsma
    Jul 13 '20 at 15:21
  • \$\begingroup\$ @Talsma it makes no sense to even think about installing a relay and a power supply to run it instead of installing a door sensor .... besides, if you insert a relay into a house alarm system, and your house gets burglarized, your insurance claim may get rejected \$\endgroup\$
    – jsotola
    Jul 13 '20 at 15:52
  • \$\begingroup\$ @jsotola: On what do you base that claim? A burglary is a burglary, regardless of how well an alarm system performs. (Of course, tampering with a fire alarm system is a whole different matter.) \$\endgroup\$
    – Dave Tweed
    Jul 13 '20 at 17:59
  • \$\begingroup\$ @DaveTweed insurance companies try to wasel out of paying claims for any small technicality ... the OP may get a discount in yearly premiums because of the presence of an alarm system ... installing a relay into that system compromises it and the insurance company could claim that the premium discount was obtained under false pretenses and that the insurance contract is null and void as a result \$\endgroup\$
    – jsotola
    Jul 13 '20 at 18:57

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