I think would go with linear/Nortek DXS series transmitters/receivers. e.g.
https://www.nortekcontrol.com/produ...less/dxsr-1504-supervised-4-channel-receiver/ You need a power supply too. I mounted everything on a DIN rail. receiver, power supply, relay modules, and Buzzer/"glue logic".
They make a specific door/window transmitter
https://www.nortekcontrol.com/produ...-supervised-universal-doorwindow-transmitter/ You might have to weather proof it bit. Here
https://www.polycase.com/product-categories is a place to start for a case. If you already have a battery out there an LT3045 based regulator could work:,
https://www.aliexpress.com/item/400...earchweb0_0,searchweb201602_,searchweb201603_
It won't be "super cheap". They have a low battery and supervision as well. Supervision can be enabled/disabled. These are used for alarm systems. I have a PERS (Medical alarm) based on their technology.
I had planned, but have not hooked it up yet to use to use a stand-alone receiver for:
A wireless doorbell
I gutted a personal transmitter and installed it in a wireless doorbell housing. Those transmitters are totally sealed. The lifetime is incredible when they are not activated.
The receiver can be configured for momentary, latch, toggle open collector outputs. I needed to add some "glue" to get relay outputs and some glue to manage the low battery audio alarm (no buzzer included) and silence functions.
Demand water re-circulator
In one case, it would go to one of their wireless motion detectors to detect motion in the bathroom and activate the re-circulator.
I had planned on using another wireless technology for the kitchen where you would press a button. Motion would not work here, but water flow sensors would. There is seldom used bathroom and a laundry room that I don't care about.
This is post where region is important because of wireless standards permitted.