Home automation

Smoke Detectors

I just recently replaced four Kidde line powered smoke detectors with Nest Protect detectors. The new Nest Protects are expensive ($99) but they are worth it. The new detectors have dual wavelength optical detectors. Each of the two optical sensors is optimized for a different range of particle sizes to cover both fast burning fires and smoldering fires.

The detectors also include a carbon monoxide sensor. Carbon monoxide sensing is important if you have a natural draft gas burning appliance in conditioned space. Operation of vent fans, whole house fans, or a blocked flue can reverse the vent flow of these appliance to allow exhaust gas into the living space. Carbon monoxide is dangerous because it is an odorless poisonous gas and natural gas combustion products are low odor.  Most carbon monoxide deaths occur at night because there are no cues to wake a sleeper.

The Nest dual optical detectors use LED light obscuration to sense smoke. Most detectors on the market are ionization detectors that use a radioisotope to ionizing the air in a cell that is open to the space being monitored. The presence of smoke increases the ionization. The current in the cell increases causing an alarm

Why I Retired the Kidde Detectors

The Kidde detectors started chirping one evening. I replaced the batteries and they continued to chirp. And they couldn’t tell me why. The Nest Detectors both Gen 1 (the flat top detectors) and Gen 2 detectors (convex top) talk to you in natural language using a recorded voice. In the US, English or Spanish language is selectable at installation. The Kidde detectors gave no indication why they were chirping after the batteries had been replaced. The Kidde manual was no help. After 20 years of this, the Kidde detectors had to go.

The Great Chili Cook

When I first installed the Nest Protects, I kept the Kidde detectors in service for a while. One evening (before the kitchen remodel) I made some chili and browned meat for it. As usual, I left the heat too high for too long, the Lodge cast iron pan overheated, and the contents began to smoke. I reduced the heat but not enough.

The smoke in the house slowly crept up. Eventually, the Nest Protects gave a heads up alert through the house announcing “Heads up, smoke in the hallway”, the near detector. Lodge pans hold a lot of heat which makes them great for searing a steak or scrambling eggs but once they are too hot, they’re going to stay too hot and smoke for a good bit.

The smoke level continued to increase to alarm level with the Nest Protects going into alarm first, then the Kidde detectors. Being traditional detectors, the Kidde detectors could do no more.

The Nest Protects had already alerted me to the increasing smoke with the heads up report and I could look for the cause. When the alarm went off, I knew which detector was in alarm and had already been notified of a potential problem by heads up message. By giving the heads up alert first, you can look for ad deal with the smoldering ash tray scenario. Knowing which detector is in alarm may influence your choice of evacuation routes.

Only One Cry Wolf Alert

One evening at 4 in the morning, one of the Nest Protects gave a smoke cry wolf heads up. I went to check the location, found conditions normal. After a bit, the detector returned to normal and there have been no further cry wolfs from it.

Why Nest Protects?

Nest Protects don’t chirp at you. Instead, they tell you in plain language why they are unhappy or confused. When an heads up or an alarm occurs, they announce the location and alarm condition in plain language. Carbon monoxide and smoke alarms have different tones.

During the installation process you connect each Nest product to your WiFi network and add it to your Nest account. Periodically, the detectors communicate with Nest. When an abnormal condition is detected anywhere in the house, all of the detectors report the condition. If you are in the den and the garage detector goes into pre-alarm, the den detector will announce the problem. If the condition worsens, the den detector will announce the alarm. A problem in one part of the house will be announced at each detector location.

Abnormal conditions include system problems and heads up alerts. Low batteries, power out, etc are announced with the heads-up message. Any smoke or carbon monoxide heads up would also be announced. A proximity detector lets the Nest Protect know that the room is occupied. This process only happens at detectors in occupied rooms.

During the installation process, you give each detector a location name from those in a list. That’s how the detector knows where it is. During the chili making incident mentioned above, the hall detector when into alarm followed by the detectors in my study and my bedroom. The third bedroom door was closed so it just followed along. as each detector went into alarm, all detectors announced the alarm and the announcements could be heard through the alarm din.

Nest Promise Feature

When you turn in at night, a light level sensor in the Nest protect senses the drop in light level. If all is well, the Nest Protect will show a green light to report that all is well. If there is a problem with any detector in the network, the detector will, instead, show a yellow ring. You can determine the issue by tapping the Nest button (big target inside the ring. The detector will announce the problem, as in “Heads up, hallway is off line”. Alternately, you can check the system status using the Nest App.

The proximity sensor will light the indicator ring with a red light during an alarm or a white light when it senses movement and the lights are out. This is a useful aid in finding the door if you have to bug out. It is also a useful indication of the greyhounds moving about to change beds. If you think a dog has come or gone, you can look for the white ring before looking for the dog who just may want to go out.

More About Installation

As a network device, Nest Protect is designed to be managed by an Android or iPhone phone and that it will be installed in a home having a working 2.4 GHz WiFi network and Internet service.


Before installing Nest Protects, you will need the following.

  • Home 2.4 GHz WiFi network operating.
  • Network name and password
  • Electrical box installed by you electrician for each wired Nest Protect
  • Electrical  safety tester, preferably electronic non-contact type.
  • Wired detector power turned off.
  • Nest IOS or Android App downloaded and installed on a mobile

Installing Nest App

Install the Nest App from the Apple iPhone App Store or from Google Play. Once installed, start the Nest app and create a Nest account. You can also view this account using a web browser at

After account creation, add a “home” giving a name, zip code, etc.

Installing a Nest Protect

Nest Protects work their magic using the house WiFi network to communicate with each other and with Nest. This means that you need a reliable 2.4 GHz WiFi network operating as a prerequisite for the installation process. With the 2nd generation detectors, installation is simple.

  1. Mount the installation ring on the wall or in-wall electrical box if the detector is line powered.
  2. With the power off, install the line powered unit’s electrical plug pig tail. White to white, black to black. Red is not used as Nest Protects use radio communications for house wide alarms.
  3. Install the Nest application on an IOS or Android device (the other prerequisite)
  4. Pull the battery tab on the detector.
  5. On the app home screen, pick the gear icon
  6. On the settings screen, tap the Add product icon
  7. On the choose product screen, tape the Nest Protect item
  8. Using the phone camera in portrait orientation, scan the QR code on the Nest Protect label.
  9. Complete the remaining screens to enter the WiFi password, choose language, and name the device.
  10. Add any additional devices to the Nest App at this time. Additional devices pick up the settings from the first added.
  11. Once network setup is complete, mount each device on its mounting ring. Interrupted screw tabs engage and hold the device to the ring. if the unit is line powered, plug in the connector before mounting it and tuck the excess cable into the box.

Nest and Legacy Detectors

The industry made a deliberate choice for detectors not to communicate from brand to brand. In fact, industry standards forbid the practice as protocol compatibility cannot be assured. So if you have a mix of Kidde detectors and Nest Protects, the two will ignore each other. The Kidde wired detectors use a third red wire to exchange alarm state. The Nest Protects use an application specific application protocol for this purpose.

Software Updates

From time to time, Nest updates the Nest App as products and product features are added and updates the device firmware to correct issues or add features. App updating is manual. Product updating is automatic. Nest will push software to all on-line devices. The Nest App device screen will show the firmware revision that the device is running.

Nest Synergy

Nest Protects come in two versions: battery powered and line powered. Both talk to you. Both talk to the Internet. An iPhone app allows you to configure and monitor the detectors. When there is a carbon monoxide alarm, your Nest thermostat receives the notification and will secure the heat. This feature has saved several lives in those homes having both devices.

The other bit of synergy is that Nest Protects contribute to the Nest Thermostat’s away or home logic. Before I installed the protects, the thermostat would go into auto away mode if I were in one room for two hours. With protects on the account, this no longer happens. The down side is that the Protects will detect the canines moving about (greyhounds) and the system will stay in home mode which they appreciate when they are home and I am out.

By davehamby

A modern Merlin, hell bent for glory, he shot the works and nothing worked.