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Internet # 100594387

Model # 21029895

Store SKU # 146421

Store SO SKU # 1000497860

Firex Hardwired Inter-Connectable 120-Volt Auxiliary Heat Detector 135 Degree with Battery Backup

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  • Heat alarm requires hardwire installation
  • All interconnected alarms will sound when one alarm goes off
  • Best for pitched elevated heat areas such as ceilings and attics
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Product Details

About This Product

The Kidde FireX HD135F is a 120-Volt AC Wire In Heat Alarm that responds to temperature rather than smoke. The alarm will sound if temperatures rise above 135 degree F. The Kidde HD135 degree F is inter connectable. The interconnect system must not exceed the NFPA (National Fire Protection Association) limit of 18 initiating devices (Smoke, heat, CO, etc.) interconnected, it is still possible to interconnect 6 strobe lights and or relay modules. This unit includes a 5-year limited warranty and is UL Listed.


  • Receive an instant alert when temperatures exceed 135 degree F
  • Test button assures proper operation of the sensor's electronic circuitry, horn and battery function
  • Interconnects with up to 24 Kidde devices (of which 18 can be initiating), including smoke and carbon monoxide alarms
  • 9-Volt battery backup provides continuous protection even during power outages
  • Red LED flashes every 30 - 40 seconds to indicate proper operation
  • Quick-connect power harness for fast and easy installation
  • Tamper-proof pin helps deter tampering and theft
  • Replacement 9-Volt battery Kidde model 21025830
  • UL/CSFM Ref. HD135F
  • Not a smoke detector
  • Compatible with Kidde, FireX, Code One and Sentinel products
  • Kidde offers a full range of 120-Volt AC wire-in life safety products with interconnect capability to provide the most immediate and complete system available; when any 1 interconnected alarm is triggered, all interconnected alarms within the home sound an immediate warning
  • Learn how to install a smoke alarm
  • UL/CSFM Ref. Kidde Part HD135
  • Click here for more information on Electronic Recycling Programs
  • Return Policy

Product Information

Internet # 100594387

Model # 21029895

Store SKU # 146421

Store SO SKU #1000497860


Dimensions: H 5 in, W 5 in, D 2 in


Product Depth (in.)

2 in

Product Height (in.)

5 in

Product Width (in.)

5 in


Alarm/Detector Features

Battery Back-Up, Hush Button, Wire-free Interconnect

Battery Type Required




Connector/Contact Type


Heat Detection Type

Fixed Temperature


No additional components or accessories are included

Pack Size


Power Source




Voltage (V)


Warranty / Certifications

Certifications and Listings

UL Listed

Questions & Answers

Q:I need to change a Firex Heat Alarm 120-1049b, preferably without changing any wiring, just plug in or use an adapter to plug in. Thank you,
by|Mar 18, 2024
1 Answer
Answer This Question

A:  Hello. No, this alarm doesn't use the First Alert wiring harness or mounting bracket and this alarm doesn't work with other First Alert alarms. You would have to change out and rewire the wiring harness and mounting bracket and you would need to take down all of the old alarms before putting up any new alarms.

by|Mar 20, 2024
    Q:Is this item NFPA-72 Compliant?
    by|Feb 29, 2024
    1 Answer
    Answer This Question

    A:  Hello. It is UL listed and can be used in locations where NFPA 72 will allow a heat detector. The unit shall at a minimum meet the requirements of UL217, NFPA72, (chapter 10 & 11 2002 edition) The State of California Fire Marshall, NFPA101 (One and two family dwellings, Federal Housing Authority (FHA), Housing and Urban Development (HUD). However, it can not be used as a life safety device. It is an auxiliary device meant for garages, attics, and crawl spaces where you can not use smoke detectors for additional building safety. The Kidde HD135F 120VAC wire in heat alarm gives you and your family an early warning to dangerous temperatures of 135˚F or more.

    by|Mar 5, 2024
      Q:Looking to replace two hardwired Firex smoke detectors S1966 120-538B. What would be comparable for that model?
      by|Feb 11, 2024
      1 Answer
      Answer This Question

      A:  Hello. There is no direct replacement for your alarms. That being said, you can use any of our current alarms to replace your older alarms. You will have to take down all of the older alarms before putting up any new alarms. You will have to change out the mounting brackets at each location but that will just take a screwdriver to change out. You will either have to change out and rewire the wiring harness plugs at each location or you can choose to use the KA-F2 adaptors to adapt the old plugs to our new alarms. The adaptors would plug into the old plugs and the new alarms would plug into the adaptors. The model for the adaptor pack is the 21028461 which includes the KA-F2 and the KA-B2 for some of the older BRK/First Alert plugs.

      by|Feb 12, 2024
        Q:Is there an app that we can use with this heat detector so it will alarm on my phone?
        by|Feb 6, 2024
        1 Answer
        Answer This Question

        A:  Hello. No, this alarm is not a Wi-Fi connected alarm.

        by|Feb 7, 2024
          Showing 1-4 of 47

          Customer Reviews

          4.6 out of 5

          • 4.6 out of 126 reviews
          • 95% recommend this product
          Filter by:
          Showing 1-10 of 126 reviews
          The Kidde Heat Alarm was easy to install. Only took...
          The Kidde Heat Alarm was easy to install. Only took about 5 min. to take down the old one and put in the new one. Also, came with a 9 volt battery which was nice. Nicely packaged and fast delivery. Didn't realize they recommend changing out detectors every 10 years.
          • Verified Purchase
          No more false alarms.
          Fumes from my Street Rod would set off my house alarm,usually at 2 or 3 AM. My son in law (ex Firefighter) told me the make heat detectors. I bought one online and it was plug and play. Took just a couple minutes to install. No false alarms since then.
          • DIY
          • Verified Purchase
          • Recommended
          1 found this review helpful
          • Verified Purchase
          Bought 14 detectors. Replacement for kidde that are 10 yrs old. Easy to replace
          • Verified Purchase
          • Verified Purchase
          • Verified Purchase
          Easy to install and setup.
          • Verified Purchase
          I would love to see a 10-year battery version of these like the rest of the lineup as the places where these go, are the hardest places to maintain.
          • Verified Purchase
          • Verified Purchase
          • Verified Purchase
          Showing 1-10 of 126 reviews