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Onset · HOBO by Onset MX1101 - Temperature/Relative Humidity Data Logger
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The HOBO MX1101 is a sensible choice if you want a small Bluetooth temperature and humidity logger you can read on your phone without opening a cabinet, and if you are willing to confirm the logging interval, memory wrap behaviour and battery type with the supplier before you commit. The listing publishes accuracy of plus or minus 0.21 degrees Celsius and plus or minus 2 percent relative humidity, a 128 KB memory holding up to 84,650 measurements, a minus 20 to 70 degrees Celsius range, 1 to 90 percent relative humidity, an LCD and Bluetooth Low Energy at up to 100 feet. It does not publish the logging interval, the battery type or life, the enclosure rating, the calibration certificate status, or the software export formats. Those omissions are not disqualifying, but they mean you should not plan a regulated monitoring job around this page alone.
The two accuracy figures, and the conditions attached to them
The listing states temperature accuracy of plus or minus 0.21 degrees Celsius in standard conditions. That phrase is doing real work. Standard conditions normally means a bench at room temperature, not the inside of a cold room at minus 18 degrees Celsius or a roof void at 55 degrees Celsius. The logger’s range is minus 20 to 70 degrees Celsius, but the accuracy figure is quoted at one point inside that range. If your job sits near either end, treat the published figure as a best case and ask the supplier for the accuracy curve across the range.
The humidity figure is plus or minus 2 percent relative humidity, described as typical and in normal range. Typical means a central value, not a guaranteed worst case. Normal range is not defined in the bullets. The logger records from 1 to 90 percent relative humidity, so the ends of that span, near condensation and near bone dry, are exactly where the 2 percent figure is least likely to hold. For most building and storage work this is fine. For a museum case or a cold store running close to saturation, it is the number you need to pin down. The site’s guide to measuring relative humidity correctly explains why sensor placement usually matters more than the headline accuracy anyway.
Memory is published; the logging interval is not
The listing says 128 KB holds up to 84,650 measurements. That is a real, useful figure, and it lets you do arithmetic the listing does not do for you. If you log one temperature and one humidity reading every five minutes, that is two measurements per interval, so 84,650 divided by two is 42,325 intervals, which at five minutes each is about 147 days. At one minute intervals the same memory lasts about 29 days. At fifteen minutes it stretches to roughly 440 days. The arithmetic is yours to check, but the principle holds: the memory is generous for slow building monitoring and short for fast process work.
What the listing does not publish is the range of logging intervals the device accepts, or what happens when memory fills. Some loggers stop; some overwrite the oldest readings. That single behaviour decides whether a logger can be left unattended for a season. If it stops, a full memory means the second half of your deployment is blank. If it wraps, you keep recent data and lose the beginning. Neither is wrong, but you need to know which one you are buying. The listing is silent, so ask. The site’s piece on how often environmental sensors should record data is a useful way to decide the interval you actually need before you ask the question.
Bluetooth range is a number; battery, housing and mounting are blank spaces
Bluetooth Low Energy with a 100 foot range is stated. That is a free-space figure in all likelihood, and walls, metal cabinets and refrigerator doors will cut it. The practical consequence is that you should plan to walk to within sight of the logger to download, rather than expecting to read it from the far end of a building. That is normal for this class of device and not a criticism, but it shapes how you deploy it.
The listing does not publish the battery type, the battery life, or whether the battery is user-replaceable. It does say the LCD shows battery status, which tells you the logger will warn you, but not how long you have after the warning. It also does not publish an enclosure rating, so there is no stated protection against dust or water. Do not assume it can go in a wash-down area or an outdoor enclosure without checking. Mounting is not described either: no bracket, magnet or strap is mentioned. For a logger that will spend its life on a wall or inside a cabinet, those small mechanical details matter more than the radio. The broader Bluetooth temperature data logger comparison covers how this class of device is usually mounted and powered.
The display changes how you use it, and the software gap changes how you finish
A built-in LCD showing current readings, battery status and logging information is a genuinely useful feature, and it is the reason many buyers pick this model over a sealed button logger. You can glance at it during a site walk and see whether the cabinet is at 8 degrees Celsius or 14, without opening an app. That saves time on rounds and catches a door left ajar before it becomes a day of bad data.
What the listing does not publish is the software side. There is no statement of the mobile app name, the desktop software, the export file formats, or whether data can be exported as CSV for a spreadsheet. For a building-monitoring job this is the difference between a logger that feeds your report and one that traps data in a proprietary view. The listing is silent, so treat export as an open question. If your work needs a documented export path, the environmental data loggers for building monitoring guide sets out what to look for.
Where the MX1101 stops being the right instrument
This is a temperature and relative humidity logger. It does not measure carbon dioxide, airborne particles, volatile organic compounds or sound. If your question is about air quality during a renovation, or about noise, this is the wrong instrument and no amount of Bluetooth convenience will fix that. It is also not an alarm: the listing describes a logger with a display, not a device that sounds or messages when a limit is crossed. If you need an alert when a freezer drifts, this logger records the drift but does not wake anybody up.
It is also not a calibrated reference. The listing does not mention a calibration certificate, and the accuracy figures are typical rather than accredited. For a regulated cold store or a museum loan agreement, you will want a certificate and a calibration schedule, which means confirming that side separately. Finally, the missing logging interval and memory-wrap behaviour mean it is a poor fit for unattended deployments longer than the memory can cover at your chosen interval. The guide to choosing a temperature and humidity data logger walks through those trade-offs in more depth.
The MX1101 is a good logger with a short published specification
Buy the HOBO MX1101 if you want a display-equipped Bluetooth temperature and humidity logger for walk-round checks and moderate-length deployments, and if you are prepared to confirm the logging interval, memory behaviour, battery type and export format with the supplier before you order. The published accuracy and memory figures are solid for building, storage and cabinet monitoring. The listing’s silence on battery life, enclosure rating, calibration and software is the part that should slow you down. None of those gaps makes it a bad instrument; they make it an instrument you should not specify from the bullet points alone.
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Frequently Asked Questions
Does the listing say what logging interval the MX1101 supports?
No. The listing publishes the memory capacity, up to 84,650 measurements, but not the range of logging intervals or what happens when memory fills. You should confirm both with the supplier before planning a long deployment.
Is the plus or minus 0.21 degrees Celsius accuracy valid across the whole minus 20 to 70 degrees Celsius range?
The listing attaches the figure to standard conditions, not to the full range. Treat it as a room-temperature figure and ask for the accuracy curve if your work sits near either end of the range.
Can the MX1101 send an alarm when temperature goes out of range?
The listing describes a logger with a display and Bluetooth access. It does not describe an alarm output or a notification service. If you need an alert, this is a recording device, not an alarm.
What battery does it use, and how long does it last?
Not stated in the listing bullets. The LCD shows battery status, but the battery type, life and whether it is user-replaceable are not published.
Is it waterproof or rated for outdoor use?
The listing does not publish an enclosure rating. Do not assume protection against dust or water. If it is going outdoors or into a wash-down area, confirm the rating first.
Does it come with a calibration certificate?
The listing does not mention one. The accuracy figures are described as typical, which is not the same as an accredited calibration. For regulated work, confirm certificate availability separately.
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