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No common wire needed, a built-in level, and the only privacy pledge on the shelf

Sensi ST55

A Wi-Fi smart wall thermostat that needs no C-wire in most homes, with a built-in level and a privacy pledge.

Sensi Smart Thermostat ST55 on a wall with button controls

Sensi ST55

A Wi-Fi smart wall thermostat that needs no C-wire in most homes, with a built-in level and a privacy pledge.

Type
Wall thermostat, wired to the HVAC system — not an outlet thermostat
C-wire
Not required in most applications
Savings claim
About 23% on HVAC energy
Installation
Built-in level and step-by-step app instructions
Form
Buttons, not a touchscreen; fits the footprint of a traditional thermostat
Privacy
The maker states it will not sell your personal information to third parties
Maintenance
Usage reports, equipment alerts, filter replacement reminders
Certification
Energy Star
Accuracy
Not stated by the maker
Amazon reference
B01NB1OB0I
EAN
0786710554827
  • No C-wire in most applications, which removes the single biggest installation obstacle on this shelf
  • The only thermostat here with a privacy commitment in writing, and the only one with a built-in level
  • The 23 per cent saving has no stated baseline, where the ecobee on this shelf names one

Best for: A retrofit where the wall has no common wire and the old thermostat’s outline must not show

≈ $100
Check price on Amazon

Specifications

Type
Wall thermostat, wired to the HVAC system — not an outlet thermostat
C-wire
Not required in most applications
Savings claim
About 23% on HVAC energy
Installation
Built-in level and step-by-step app instructions
Form
Buttons, not a touchscreen; fits the footprint of a traditional thermostat
Privacy
The maker states it will not sell your personal information to third parties
Maintenance
Usage reports, equipment alerts, filter replacement reminders
Certification
Energy Star
Accuracy
Not stated by the maker
Amazon reference
B01NB1OB0I
EAN
0786710554827

What the maker puts in writing

  • C-wire not required in most applications
  • About 23% saving on HVAC energy, Energy Star certified
  • Built-in level and step-by-step app installation
  • Buttons, same footprint as a traditional thermostat
  • Will not sell your personal information to third parties
  • Usage reports, equipment alerts, filter reminders

The C-wire is the real decision on this shelf

Four thermostats here demand a common wire. Three work without one. That single fact decides whether the job is a twenty-minute swap or an electrician.

This is the most expensive of the three that do not need it, and the one that publishes most about why the install is easy.

A sentence nobody else writes

Sensi won’t sell your personal information to third parties.

A smart thermostat learns the hours a house is empty. Eight other listings on this shelf say nothing about what happens to that.

Availability

Read on the day this page was built: $100 at the American Amazon shop.

Read from Keepa on the day this page was last revised; stock and price both move without notice.

Prices quoted in this text were read on 2026-10-04. The live price is at the top of the page.

The questions that keep coming up

Really no C-wire?

In most applications, by the maker. Four thermostats on this shelf require one outright and say so in capitals, and two more work without it on most systems. If your wall has four wires, this is one of three thermostats here that should still work.

Why does a built-in level matter?

Because a thermostat mounted crooked is visible forever on a flat wall. It is a small thing and nothing else on this shelf includes one.

What is the privacy statement worth?

It is a published commitment not to sell personal information to third parties, which is the only such line on this shelf. A smart thermostat knows when the house is empty; that is worth a sentence, and eight listings here do not give one.

More outlet thermostats

  • Suuwer non-programmable thermostat with blue backlit display on a wall

    Suuwer S701

    A non-programmable single-stage wall thermostat with a 0.2-to-2 °F swing, a selectable five-minute compressor delay and ±1 °F accuracy.

    Type
    Wall thermostat, wired to the HVAC system — not an outlet thermostat
    Systems
    Conventional single stage, up to 1 heat and 1 cool: gas, oil or electric furnace, ventilation and air conditioning
    Not compatible with
    Multi-stage (1H/2C, 2H/2C), heat pumps (2H/1C, 4H/2C), PTACs, 3-wire hydronic, dual fuel, 120–240 V line voltage, mini splits, RV Mach and Roughneck series
    Power
    24 V AC or 2 AAA batteries; no C-wire on most systems
    Swing
    Separate heating and cooling, 0.2 °F to 2 °F
    Compressor delay
    5 minutes, selectable on or off
    Accuracy
    ±1 °F, with room temperature calibration
    Ranges
    Display 41–95 °F; control 44–90 °F
    Warranty
    2 years
    Amazon reference
    B07WTDPPRX
    EAN
    0709327753278
    • The only thermostat on this shelf that publishes a swing range — 0.2 to 2 °F — which is the setting that governs how evenly the house is heated
    • A selectable five-minute compressor delay, which protects an air conditioner from short-cycling and which nothing else here publishes
    • Non-programmable: no schedule, no app, no voice

    Best for: A single-stage system where the owner wants to tune the cycle rate and protect the compressor

    ≈ $27
    Check price on Amazon
  • ChiliTec ST35 plug-in outlet thermostat with analog rotary dial

    ChiliTec ST35

    ChiliTec's ST35 is an analog plug-in thermostat rated 230 V, max. 16 A / 3,500 W, switching a connected heater or fan on and off around a 5–30 °C (41 to 86 °F) setpoint in 1 °C steps. A slide switch sets heating or cooling mode, and the sensor is built into the plug itself rather than an external probe.

    Max. load
    230 V, 16 A, max. 3,500 W — stated by ChiliTec
    Temperature range
    +5 °C (41 °F) to +30 °C (86 °F), adjustable in 1 °C steps
    Switching behavior
    ±1 °C (34 °F) threshold, 10-second measurement interval, with a delayed reading ChiliTec says is meant to stop the relay tripping on a passing draft
    Mode switch
    Slide switch between heating and cooling; the connected device is driven in whichever mode is selected
    Sensor
    Internal — reads the air at the plug, not a remote probe
    Protection rating
    IP20, indoor use only
    Dimensions / weight
    H 128 × W 68 × D 39 mm (5.04 × 2.68 × 1.54 in) as plugged in; 190 g
    Amazon reference
    B01MZFKWS5 (EAN 4250416312457) — live offer confirmed on DE/FR/IT/ES; listed with no live offer on GB, no ASIN found on US, at check time
    • 3,500 W / 16 A rating is published by name, not left to be inferred from the plug
    • A heating/cooling slide switch means the same unit can drive a fan or a cooling device, not only a heater
    • Internal sensor only — it reads the air right at the socket, which runs warmer than the middle of the room once a heater has been on for a while

    Best for: Adding a numeric-ish setpoint to a heater or fan that only has a low/medium/high dial, in a dry room where the socket sits close to where you actually want the temperature held.

    Search Amazon for this model
  • Elektrobock TS05 digital plug-in outlet thermostat with LCD display

    Elektrobock TS05

    Elektrobock's TS05 is a digital plug-in thermostat with a relay output stated as max. 16 A, switching a connected heater between +3 °C (37 °F) and +40 °C (104 °F) in 0.5 °C steps, with a frost-protection floor at 3 °C (37 °F) and settings that Elektrobock states survive a power cut.

    Max. load
    230 V / 50 Hz, relay output stated as max. 16 A — Elektrobock does not publish a watt figure directly; at 230 V that computes to about 3,680 W
    Temperature range
    +3 °C (37 °F) to +40 °C (104 °F), adjustable in 0.5 °C steps
    Hysteresis
    0.5 °C (33 °F), with a stated measurement accuracy of ±0.5 °C (33 °F)
    Frost protection
    Built-in, engaging at +3 °C (37 °F)
    Power-cut behavior
    Retains its settings through a power outage and resumes automatically, per Elektrobock
    Protection rating
    IP20; stated operating range 0 °C (32 °F) to +40 °C (104 °F) ambient
    Display
    Digital, with + / − and ON / OFF buttons
    Amazon reference
    B00YURX7BI (EAN 8594012221703, plus three further regional EANs on the German listing) — sold and shipped by Amazon on DE at the time we checked. A catalog page exists on FR/IT/ES/GB under a different ASIN (B01BVKTFXU) but carried no live offer or price on any of the four at check time; no listing found at all on Amazon US
    • Widest and coldest-reaching range of the three outlet thermostats in this hub: +3 °C (37 °F) to +40 °C (104 °F), against +5 °C (41 °F) to +30 °C (86 °F) on the ChiliTec ST35 and the McPower TCU-330
    • A stated frost-protection floor at +3 °C (37 °F), which neither of the analog units in this hub publishes
    • States its output as "max. 16 A" rather than a watt figure — the 3,680 W equivalent is our own arithmetic at 230 V, not a number Elektrobock itself publishes

    Best for: A cold garage, shed, or outbuilding where frost protection and a wide temperature range matter as much as the day-to-day thermostat function, and where settings surviving a power cut is worth having.

    Search Amazon for this model

Elsewhere in the spares drawer

  • Acfun universal air conditioner remote control with LCD display

    Acfun Acfun

    A universal LCD air conditioner remote with automatic code search and an 8-to-10-meter range, excluding window and portable units.

    Type
    Universal, LCD, with digital automatic code searching
    Claimed coverage
    Over 1,000 air conditioner brands
    Does NOT work with
    Window or portable air conditioners — stated twice
    Also excluded
    Frigidaire, Mitsubishi, Sanyo, and Sharp AF-Q60RX
    Range
    Approximately 8 to 10 meters (26 to 33 ft)
    Batteries
    2 × AAA, not included
    Manual
    English, in the package and in the listing images
    Programming
    Required — automatic code search
    Contradiction
    The title lists Mitsubishi as supported; the fifth bullet lists it as unsupported
    Amazon reference
    B07DN9PYKQ
    EAN
    0656516056903
    • The only remote on this shelf that publishes a working range: approximately 8 to 10 meters (26 to 33 ft)
    • The lowest price here, with an automatic code search and an English manual included
    • It does not work with window or portable air conditioners, which is most of what this site covers

    Best for: A wall-mounted split or ductless indoor unit from a brand not on its exclusion list

    ≈ $7
    Check price on Amazon
  • AZBME replacement remote control for Fujitsu air conditioner with LCD display

    AZBME Not stated by the maker

    A Fujitsu replacement remote covering more than fifty unit codes, showing both temperature scales, with a luminous mode.

    For
    Fujitsu AR-RAH2U and AR-RAH1U, with over fifty ASU, AOU, AUU and Ar-Ry unit codes listed
    Display
    Fahrenheit and Celsius
    Luminous mode
    Yes — usable in the dark
    Materials
    Recyclable ABS body with soft rubber buttons
    Batteries
    Not included; AAA 1.5 V
    Type
    IR remote
    Universal
    No — model specific
    Programming
    Not stated by the maker
    Amazon reference
    B0FDH6MRZB
    EAN
    0733723740891
    • The only remote on this shelf with a luminous mode, which is the whole problem with a bedroom remote at two in the morning
    • Publishes both temperature scales, where one remote here is Celsius only and seven say nothing
    • Fujitsu only: the code lists are long but they are all one brand

    Best for: A Fujitsu wall or ceiling unit, especially in a bedroom where the remote is used in the dark

    ≈ $17
    Check price on Amazon
  • fosa universal air conditioner remote control for R51 series

    fosa fosag9mauow4v8

    A replacement for the R51M/E and the wider R51 series, with a built-in clock and on/off timers and no setup required.

    For
    R51M/E, and the R51 series: R51/E, R51/CE, R51M/CE, R51D/E, R51M/BGE
    Programming
    None required
    Clock
    Built in
    Timer
    On and off
    Display
    Screen, described as easy to operate
    Power consumption
    Described as low; no figure given
    Batteries
    Not stated by the maker
    Range
    Not stated by the maker
    Amazon reference
    B07G75B1GQ
    EAN
    0700890210083
    • Covers six R51 variants, which is the remote family used across a very large number of machines
    • No programming or setup, published, so it works as soon as batteries are in
    • Publishes no range, no battery type and no display scale

    Best for: A machine whose original handset is marked R51 in any of its variants

    ≈ $9
    Check price on Amazon

All outlet thermostats