Remotely (wireless) triggered alarm with two (or more) alarmsignals

Hi, I'm planing to build an alarm that will be used to signal 'in urgent need of assistance' or 'in need of assistance'. The current system used by my client only has one alarmsignal, which is not ideal.
I would like to get your opinion on how I should use to make this build secure and stable.
The alarm needs to use wireless communication that works between 2 stories, consist of a 'base station' with speaker(s), base (and remote if possible)have both battery and wired power, minimum risk of interference from other transmitters.

List of hardware I currently have on hand:

  • Arduino Nano
  • Arduino Uno R3
  • Digispark Tiny85 - link
  • WeMos D1 Mini - link
  • XD-RF-5V
  • XD-FST
  • CATALEX MicroSD Card Adapter v1.0 - link
  • NRF24L01+ - link
  • HM-11 BLE Bluetooth 4.0 Transceiver CC2541 JDY-10 - link
  • RF Remote transmitter and Receiver Relay board (Note: Remote works together with XD-RF-5V) - link
  • MP3 Player Module Board - link

What do you think would be the best setup?

If "urgent" is a real requirement, then you need to include the requirement for continuous power of all pieces and have periodic self testing of the communications link and activating components. Say, once per minute?

Paul

For the communications, both the NRF module or WiFi could work - you have to try which one gives you the best signal through the walls and ceilings. Bluetooth is less likely to work.

Secure has many levels. It can be secure from accidental power disconnects to intentional disabling to fires or bombs. Set your requirements here. I can imagine you don't need to make it bomb proof as in that situation there's nothing left to raise the alarm over, but you'll have to say how far you want to go.

Regular pings between the two are indeed a good idea to see if the other side is still alive, but the same accounts for the side that has to raise the actual alarm, it has to have some form of fail safe. What about you don't notice the wall wart dies, and a few days later the backup battery runs out? No power left to even sound the alarm.