Review of Onzo energy monitor

turning-off-lights-to-save-electricityAs you might be aware, we’ve been reviewing an Onzo electricity monitor. We’ve been taking part in a ‘carbon fast’ as suggested by Reduce Footprints and as it happened, this monitor had arrived the day before.

Reducing our electricity consumption is something Mr green and I have been talking about again! and this has been the perfect excuse and motivation to get started.

For some reason allowing our electricity usage to creep up is something we keep doing. Old habits die hard it would seem.

I’m going to do 4 reviews on the Onzo. Today’s will be my initial thoughts from when the Onzo monitor arrived to setting it up. Next weeks review will be about ‘living with an Onzo monitor’ and I’ll tell you how easy, effective and useful the unit is. The third review will be about syncing the device to your computer and the last one will be a review of how much energy we have saved (or not!)

The monitor arrived on a Tuesday morning so we decided to have a ‘normal’ week to see how much we can save by making small changes to our lifestyle.

Just so you can create a picture in your mind; at Chez Green we do not have gas. We use electricity for cooking, back up heating and the immersion tank. We have a woodburner for heat and it will heat the water, but I pop an electric heater on in our bedroom each night and if I work upstairs during the day I use a convector heater. We run LED light bulbs downstairs which use solar. During the summer when the woodburner is not being used, we have to heat water with electricity. What this often means is our electricity consumption is pretty much the same throughout the year. During the winter we cook more but get ‘free’ hot water most of the time, and in the summer we need to use electricity for water but cook less.

Here are my initial thoughts with setting the Onzo monitor up. As well as something that helps reduce energy consumption and therefore my carbon footprint, I look at other features such as materials used for the product and packaging along with any other eco friendly features.



Great packaging – the Onzo arrives in a slick cardboard box with a small amount of polythene; all of which can be recycled.

Battery. The unit comes with a recyclable battery which is easily charged. This is a fantastic feature as we have used energy monitors before which have eaten disposable batteries.

Display. The display tells you everything you want to know – either power usage or running cost. You don’t need anything else and this has been well thought out to make it easy to toggle between both displays.

Interactive. The monitor gives you a daily target based on your average usage. This adds real incentive to using the monitor.

Tracking. The Onzo tracks your electricity consumption by the second. Some monitors take a while to ‘see’ that you have turned the kettle or shower on, but with Onzo, it’s instant.

The display is extremely good quality and very durable, it’s almost like a big child’s toy!

recyclable cardboard packaging from Onzo

recyclable cardboard packaging from Onzo


Silica Gel. A sachet of silica gel will end up landfilled unless I reuse it.

Wall charger. We couldn’t find the wall charger anywhere and I realised it was still in the outer box. I can seriously imagine some people throwing it away by accident. The packaging is wonderful but there is nowhere for the charger to sit which seems an oversight.

Ease of setting up. If you take a moment to look something up when you’re setting the monitor up, it goes back to the beginning. This means, if you look for your unit charge and take too long finding it, you have to scroll through the currency charge, date and time AGAIN before being able to enter the unit charge. This is just plain frustrating.

Estimating averages. I have two charges on my tariff. The first 85 Kwhs per quarter at once price and the rest of my usage is at another, lower price. There is no way to account for this with the monitor, so I had to guess at my unit price by estimating an average.

Transmitter clamps. It was fine for me, but the transmitter that clamps onto the wires coming into your house are huge. For some people they would probably not be able to fit the transmitter on.

Back of display. The back of the display doesn’t stay on properly. It’s fine for us with an older child, but wouldn’t be good for a family with young children as they would have access to the battery and display controls.


Setting buttons. Oh man, the setting buttons are So hard to use. I thought of my friend Gennie who has arthritis and there is no way she would be able to use them. I ended up with a really sore finger after setting everything – I sound a wuss, but it really did hurt! I understand you don’t want to be able to accidentally change a setting, but really, these were too hard to push.

Set to zero. The standing charge is set to £20. Mine is zero and I had to scroll through *in pennies* to set it to zero – a ‘set to zero’ button would be a huge help.


I’ve now set up three different energy monitors and the Onzo does have much clearer and easy-to-follow instructions. You’re told what you will need beforehand (access to old bills and current tariff) and are talked through each step. Apart from a few blips it was pretty straightforward. The packaging is excellent and they’ve paid attention to using boxes which will fit through a standard letterbox which means if you’re out when it is delivered, you’ll find it waiting for you when you get home – no having to queue at the post office for your ‘undelivered’ item. The display looks very durable and should withstand a few knocks.

My main concern is with how difficult it is to press the setting buttons and the omission of a simple function such as ‘set to zero’.


  1. Small Footprints on March 21, 2011 at 8:51 pm

    Wow … great review! I really appreciate that you include the “real world” setup of this device … sometimes those factors can make or break usage. Looking forward to the next 3 reviews. 🙂

  2. Colin Barrett on June 4, 2011 at 5:11 pm

    We would be very interested to make contact with other users of the ‘Onzo’ as we have an issue with a 2, sometimes 4kw ‘peak’ that occurs in our house at roughly 3-hourly intervals; day and night, even when we are not in residence!

    We think it may be a fridge/freezer but wonder if anyone else has seen anything like it, i.e. could it be an installation issue or a faulty Onzo?

    We can be contacted via our website:-

    Best regards, Colin & Urszula Barrett

  3. Mrs Green on June 12, 2011 at 8:10 am

    @Colin Barrett: Hi Colin, welcome to the site; what a strange thing to have this peak! Do you have an immersion heater that comes on to top up hot water?

    Fridges and freezers (unless you’re running a business with a lot of them) would not use this much power; and as they cycle on and off it would only be a 5 minute peak…

  4. GUS on June 20, 2011 at 3:54 pm

    Sounds like an immersion cycling @Colin Barrett:

    & possibly in combination to this possibly a freezer that seriously needs defrosting to improve it’s efficiency, thus the rapid cycling on top of your base load (which you didn’t mention) a pure guess.

    An immersion is around 3Kwh pull (like a kettle), is it properly lagged & what size is it, how often do you draw water off etc, all this will affect the amount of big loads your onzo displays as pulling.
    check for underfloor heating being on out of season too just in case!

    Our HW tank for example is around 125 litres, old probably very scaled up (reduced efficiency, despite using a descaler) & it is on 65c left on 24 hrs, cycles typically 15 minutes 4x per day, pretty well lagged to retain heat.
    look around if you’ve got the monitor you can find it & why it’s high!

  5. Mark Brock on October 19, 2011 at 8:01 pm

    @Colin Barrett:

    Our fridge cycles roughly twice an hour, and on about a quarter of the cycles shows a sharp peak at the start of the running period. I believe fridge compressors use induction motors which have a high starting current. It the Onzo happens to sample the current just as the fridge compressor starts up, it would register that high power value even though it will very quickly reduce to, in my case, about 300W. So if your peaks are, like mine, just a spike – then I think it is just a characteristic and doesn’t indicate any problem.

  6. James on March 17, 2012 at 9:39 am

    Re set to zero & standing charge.
    I think the reason the have not given a set to zero is that everyone has a standing charge, but it is sometimes hidden in your tariff, you need this to accurately predict the costs.
    “The reality is that all electricity tariffs incorporate a standing charge, which for split rate billing is simply hidden in the initial higher rate per unit. You can calculate your own standing charge by subtracting the low rate from the high rate and multiplying the result by the number of units to which the high rate applies. If the number of higher rate units is quoted as an annual total, you divide by 365 for the daily rate. If the higher rate units are given for just a quarter, you divide by 91.”

  7. Mrs Green on March 19, 2012 at 5:52 pm

    @James: thanks for the info James – that was most helpful 🙂

  8. Bungy on March 30, 2012 at 1:19 pm

    I have an ONZO smart energy monitor but the battery failed. Lekky company sent me a new one and ran through the setup process to install the new battery. All sorted until one day I noticed the back was off and the battery pack had pinged out of place. I now have batt err on the display and dont know how to flash it back up again as I no longer have the battery replacement instructions….! Can anyone tell me the process please….


  9. Mrs Green on April 1, 2012 at 3:08 pm

    @Bungy: Hi Bungy, I have no idea I’m afraid – have you contacted Onzo direct? I probably have a contact there if you still need help – let me know!

  10. Richard Powley on June 8, 2012 at 7:08 pm

    @Mark Brock: The peaks are quite normal when the fridge/freezer turns on. It is simply the switching current on the thermostat turning the appliance on.(Manufacturers usually save on using a “zero phase”, switch). The real power used when the fridge/freezer is on is only about 50 watts. The ONZO shows peaks here during the night but I disregard them.

  11. Andy on June 16, 2012 at 9:07 am


    The original 3 cell re-chargable battery pack in the Southern Elec Onzo meters connected via a mini twin lead and connector and just one end (negative) of the first cell of the pack was exposed to make contact with the spring. They were very short lived (mine only lasted 4 mths) and you can then use 3 individual disposable or normal re-chargable AA cells that you place in the compartment and they connect via the springs and don’t have a little red lead and connector. It was a nifty way of being able to recharge the special Alkaline rechargable 3 pack (made by PURE) or use individual AA cells without the Onzo trying to re-charge them. You have to re-charge NiMh or NiCad outside in a separate charger. I run mine on NiMh AA cells and pop them in a re-charger when I am doing the upload to my PC each week or so.

    As of June 2012 Southern Electric were sending 3 plain alkaline batteries to all their Onzo users with a letter asking them to remove the supplied 3 cell re-chargable alkaline battery pack and dispose of it. They suggest you run the Onzo via the usb lead connected to your PC or the original supplied mains charger. This does not suit me as I have mine on the wall – hence the use of re-chargable AA cells.

    Hope this helps.

  12. Brian on September 5, 2012 at 11:54 am

    Scottish & Southern Electricity Co sent me Monitor in May. I am very please and all was working until toady. The Rechargable Batteries in the Sender Failed overnight, I have researched the numbers on the pack to no avail. Do you know where I can source replacements please? SSE say they no longer send out replacement batteries, but could send out a replacement complete unit, but I would loose all data and have to start again. I have contacted ONZO Direct by e-Mail as they are not answering their phones. Personally I think they should send me replacement Batteries as the unit is less than one year old, although I do not have any proof of purchase. Any thoughts/ideas would be welcomed, has anyone else experienced a similar problem?

  13. Andy on October 20, 2012 at 10:07 am

    Having trouble posting here now. It says enable Javascript and cookies and then in the diagnostic page that pops up it says
    Javascript enabled
    Cookies enabled.


    It just lost my reply to an earlier post..

  14. Andy on October 20, 2012 at 10:13 am


    I wonder if Southern Electric were answering the question they expected you were asking.. ie “can I have replacement battery for my display” as they have had ongoing problems with the rechargable Alkaline battery pack in the display failing after just a few months and up to earlier this year used to send out replacement batteries all the time.

    On the problem you are having with the sender I wonder if it would not be best to accept the offer of a new sender. If the battery in your one has totally failed it may have lost any saved data anyway so putting in a new battery would not bring it back.

    I would just for good luck try re-syncing the display and sender (instructions in the manual) and then just try one last time to upload to the iplan website then swap over to the new sender if they will send you one.

  15. Andy on October 23, 2012 at 2:16 pm

    Update: I don’t believe it. Just 3 days after posting about the batteries in the sender mine failed this morning. As I was checking the display it kept putting up the T symbol for poor reception. Downloaded what I could and looked at the sender to find the AAA battery pack had failed and leaked out into the compartment. Southern Elec helpline said they would send out a new sender and to dispose of the old one. May take some time they said. Not wanting to have a break in my energy monitoring I carefully cleaned the unit and put in 3 AAA normal batteries and it is working again – but for how long I wonder?

    I also dismantled the rechargable battery pack by taking off the plastic heat shrink covering. Simply 3 AAA cells joined nose to tail. The tail end (-ve) is exposed to make contact with the spring. The head end (+ve) is connected to BOTH of the red leads that go to the little connector and is then insulated with the heat shrink.

    So this is how the sender (and I guess the display as well) knows if it is running on rechargable alkalines or simple primary alkalines. If the +ve is connected via the little lead and two pin connector then it is rechargable pack. If the +ve is connected to the spring terminal then it is primary. So the unit can draw juice from either of these two places but only attempts re-charging via the lead. Thinking of trying to make a pack of NiMH cells and trying that in the old unit once the new one arrives.

  16. Colin Barrett on February 5, 2013 at 1:37 pm

    @Mark Brock:Mark, thanks for your response and apologies for not coming back sooner to read this. It is indeed the fridge/freezers causing the spike(s). We’ve a freezer in the garage and combi in the kitchen.

    Having identified it we are less worried but the initial graphed spikes caused me to think that the fridge was heading for melt-down and possible major fire in the house.