The HVAC Smart Relay Switch (HSRS) is an energy saving device designed to automatically shut off air conditioning or heating when a monitored door or window remains open for a preset period of time. Available in both wired & wireless packages, the system uses compatible door/window sensors – two included. For the wireless edition, choose one of the following product generations:


  G3-Mini G3-Basic G2-Classic
RF Range 75 ft. 75 ft. 100 ft.
Battery CR2032 CR123A AAA (x2)
Dimensions 2.2″ x 1″ x 0.25″ 3.1″ x 1.6″ x 1.2″ 3.25″ x 1.5″ x 0.5″
Wired input
No Yes
Mounting tape tape+screws tape+screws
Feature Specs


  • GEN2 – Our second generation (classic) sensors feature a wireless RF transmission range of 100 ft. Requiring two (2) AAA batteries (not included), they are auto-addressable (up to 65,000+ possible IDs) and measure 3.25″ x 1.5″ x 0.5″. Foam mounting tape and screws are supplied. (GEN2 sensors do not store a permanent address and therefore must be initialized and re-registered whenever batteries are replaced.)
  • GEN3 – Our third generation sensors are available in two models: mini and basic. The mini sensor has a wireless transmit range of 75 ft. and operates on a single CR2032 lithium coin-cell (included). The basic sensor has a wireless range of 75 ft. and includes a CR123A cell. Each is pre-programmed with a unique, permanent address (over 16 million possible IDs). The mini sensor measures 2.2″H x 1″W x 0.25″D and includes foam mounting tape (no screws). The basic sensor measures 3-1/16”H x 1-9/16”W x 1-3/16”D and includes foam mounting tape and screws.


FAQ: Which is better for me, GEN2 or GEN3?
  • Notes:
    • The two product generations are not cross-compatible as they operate on different radio frequencies. Therefore, a 2nd generation controller will not accept a 3rd generation sensor. Nor will a 3rd generation controller recognize a 2nd generation sensor.
    • G2-classic sensors feature a copper coil antenna for excellent transmission range (100 ft).
    • Both G2-classic and G3-basic sensors provide wired contact screw terminals for optional external wired switch (N/C) or closed contact loop. Unless you plan to utilize this input, it must be disabled to avoid inadvertent trigger. To disable, simply apply a short jumper wire across the wiring terminals.
    • RF range values are based on ideal conditions in open space. Actual results will vary for every installation. In general, wireless signals can be diminished or impeded by RF interference, concrete walls, large appliances, etc.


  FAQ: Tips for a proper install?


The HSRS is fully configurable using onboard DIP switches, allowing you to establish specific operational parameters. For instance, configure the device to temporarily disable the air conditioning or heating system when any door or window has remained open for 10 minutes and then re-enable when the door has remained closed for 1 minute. (Requires installation by a qualified hvac technician.


FAQ:  Wireless sensors on metal doors & patio doors?



  • Automatically shuts off air conditioning or heating when a monitored door or window remains open too long
  • Accepts wired and/or wireless sensors types – two (2) included. (For additional sensors, see “Related Products” at the bottom of this page.)
  • Configurable delay period using onboard DIP switches, up to 10 hours
  • Expandable (accepts up to 4 wired zones and/or 8 wireless sensors)
  • Ideal for split (central) a/c systems
  • Compatible with most existing thermostats

(Note: Installation by a qualified hvac technician is recommended.)


FAQ:  Is it safe for my A/C compressor?


What’s Included:

  • HSRS controller with mounting flange
  • Two (2) door/window sensors. (For additional sensors, see “Related Products” at the bottom of this page.)
  • Power converter (24 vac)
  • Integrated RF receiver (wireless systems only)
  • Whip antenna (wireless systems only)
  • Warning decals – see below:



  • Though installation is not difficult, a qualified HVAC technician is recommended.
  • System includes two (2) door/window sensors. (Add-on sensors also available.)
  • Wireless sensors are battery-operated.


Video Tutorials:


Additional Info:




Installation Guide:


Full User Manual:


Using Wireless Sensors on Patio Doors:


Other Resources:


Ask a Question


Contractors / Resellers

Weight 3 lbs
For HVAC system

Central (split, ducted), Mini-split (ductless), Packaged (rooftop, etc.), Fan coil, PTAC, Window unit, Other (pls contact us)

Door/window sensor

Wireless classic (GEN2), Wireless mini (GEN3), Wireless basic (GEN3), Wired

Sensor quantity

2, 4 (+$85), 4 (+$59)

Will a metal door interfere with wireless sensor operation?

Many types of metal doors, windows, and patio door frames can interfere with the operation of a wireless door sensor, severely undermining the RF signal. The sensor may operate flawlessly prior to installing the unit. But once mounted to the door or frame, there may be little, if any, detected signal at the controller / receiver.

Does the problem affect all wireless door sensors?

While most any wireless door sensor may be subject to this kind of impediment, our GEN2 "classic" sensor is designed with a copper coil antenna that makes it less susceptible, though not completely immune.

Is there a viable solution?

Fortunately, there is a relatively simple approach for combating the problem. Click here for details.

Which wireless system should I choose? (GEN2 vs GEN3)

Our HSRS wireless systems are available in two generations: GEN2 & GEN3. While both are functionally equivalent, there are some key differences to consider when making your purchase. (Bear in mind that the two generations are not cross-compatible. Therefore, you may not use a GEN2 sensor with a GEN3 controller, or vice-versa.) The two product generations are discussed below.

For a comparison summary, scroll to the bottom of the page.


Manufactured by Honeywell, these sensors are the same type found in compatible security systems. They feature sleek, modern design and long battery life (batteries included). We offer two GEN3 sensor models: mini and basic. Both operate at 345 MHz, and are advertised with a transmission range up to 200 ft. (open air). However, we have found the usable range is typically lower and can vary widely from one installation to the next. (The RF signal can be diminished by some types of metal door framing.) Therefore, you should presume a max range of 75 ft. GEN3 sensors store a factory-assigned ID (address) and need only be registered (i.e., paired) once at the controller/receiver.


Tried and true, our GEN2 classic (X10) sensor has withstood the test of time. Operating at 310 MHz and featuring internal copper-coil antenna, this device packs a wallop. Less susceptible to signal degradation issues, it yields a usable transmit range up to 100 ft. The sensor stores a random, self-assigned ID (address). Therefore, re-registration at the controller is required whenever batteries are replaced. Two (2) AAA batteries are required, delivering up to 2 years of reliable operation. Lithium batteries will last 5 years or longer!

Comparison Chart:

The chart below compares critical features of the two wireless product generations:

    GEN3   GEN2
  • Modern design
  • Permanent ID (address)
  • Battery included
  • Copper coil antenna
  • Excellent range (100 ft.)
  • Diminished range
  • Temporary ID (address)

What is the current-switching capacity?

The Kadtronix family of smart relay systems are rated as follows:

  •   5A @ 125vac

Any tips for completing a proper install?

Installation is straightforward and requires no special skills other than your existing expertise with HVAC systems and basic wiring. Consider the following tips for a smooth, trouble-free installation:

Tip #1: When installing the HSRS wireless system, be careful to avoid contacting the antenna to any grounded surface such as the HVAC equipment chassis.

Tip #2: For best RF reception, locate the antenna as high as possible (i.e., just below the ceiling). Also, ensure a minimum separation of 3 feet from any of the following:

  •   - Wireless devices (wi-fi routers, cordless phones, etc.)
  •   - Metal equipment (HVAC, laundry appliances, water heater, metal shelving, etc.)

Tip #3: Before permanently mounting wireless door/window sensors, first complete the registration (i.e., pairing) procedure, keeping the sensors close-at-hand for convenience. Following registration, test to ensure the controller unit recognizes door sensor activity. Once you are satisfied the system is behaving properly, apply the sensors as desired.

Tip #4: When installing a wireless door/window sensor, consider the following:

  • - The mini sensor requires no setup other than inserting a CR2032 battery (included)
  • - The basic sensor contains two wiring screw terminals which must be wired together with a short jumper. Apply the jumper prior to inserting the battery. (The jumper can be omitted if you plan to apply a wired door switch at these wiring terminals.)
  • - The classic sensor must be properly initialized after inserting batteries. To do this, press & hold the white push-button for 5 seconds.

Is it safe for my A/C compressor?

Absolutely! First, consider that modern HVAC systems are equipped with built-in delay mechanisms to ensure that refrigerant pressures have equalized before allowing the compressor to start. Second, our HSRS controller features its own configurable delays, described below:

Delay #1 minimizes the possibility of short-cycling by preventing shut-off unless the monitored door or window remains open for a preset time period. Configurable from 0 to 600 minutes (10 hours), the typical setting for most installations is 2 minutes. Therefore, a door must remain open continuously for 2 minutes before shut-off is invoked.

Delay #2 is a configurable re-activation timer that prevents the HVAC system from restarting until the desired time elapse. As mentioned earlier, most HVAC systems provide their own built-in delay for this purpose, so a secondary delay is typically not required. Still, we find that some customers prefer to deploy it for added peace of mind.