Updated 06JUN21 - Smart Plug Vampire Power Draw Shoot-Out

UPDATED June 20th, 2021
Updated firmware on 6/20/2021.
These values were measured with a Kill A Watt P3.
These values are simply the plug on/off without anything connected to the smart plug to see the vampire draw.
Values could slightly vary with the distance between the plug and your wifi access point:

TP-Link HS300
Hardware ver 1.0
Firmware ver 1.0.20

LEDs on / LEDs off (status LED setting in Kasa App)
4.00W / 3.70W - 6 plugs on
3.40W / 3.20W - 5 plugs on
2.90W / 2.70W - 4 plugs on
2.40W / 2.25W - 3 plugs on
1.85W / 1.75W - 2 plugs on
1.35W / 1.25W - 1 plug on
0.85W / 0.85W - all plugs off (only the 3 USB ports are powered, as always)

TP-Link: KP115
Hardware ver 1.0
Firmware ver 1.0.17
on: 1.25W
off: 0.65W

TP-Link: HS110
Hardware ver 1.0 (without USB socket)
Firmware ver 1.2.6
on: 2.00W
off: 1.45W

Belkin: WeMo Insight 79F (discontinued)
Hardware v2
Firmware ver WeMo_WW_2.00.11532.PVT-OWRT-InsightV2 (discontinued)
on: 1.8
off: 1.3
WeMo Insight stays off after a power outage is restored – I found this useful in an application
TP-Link HS300, HS110, & KP115 return to last on/off state after a power outage is restored – mostly preferred

Maybe someday I’ll get my hands on a HS110 HW ver 2.0


Nice work @MachoDrone ! I like what you have done, but the Kasa KP115 is the new power-sensing workhorse from TP-Link. It functions similarly to the HS110, but has a smaller profile (doesn’t block the second outlet in the wall), but has also seen a few connectivity issues with the Sense monitor if you look around on Community. For me, my single KP115 has shown as much reliability as the HS110s, and it’s 2 of my 3 HS300s that have surprised me with connectivity issues a few times.


i’ve been lucky with my HS300s and HS110’s. My success with these may be that i have a dedicated 2nd Access Point for the Smart Plugs and Sense Monitor wired to the back of my main Wireless Router. The main wireless router is used for the rest of the property.
I have like 15 HS110 smart plugs and 6 HS300 power strips.
imma checkout that KP115, appreciate it.

Question in regards to on vs off: is that that the smart plug is off but plugged in, or that the device plugged in to it is off but the smart plug always remains on?

I’d like to hear energy usage of the new KP115 to see if it’s the same, better, or worse than the 110.

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@brian5 , i’ll have my hands on a KP115 this weekend.
i’ve been really curious about the vampire draw with all my plugs… i’m not worried, overall… my home consumes tons of power.
these tests are only the smart plug on/off without anything plugged into it.

Well this could explain why I can’t identify all of my always on devices. My 41 smart plugs alone add approximately 75W. Nice work.


Very nice data, @MachoDrone, thank you for this post!

I had taken some similar measurements a year and a half ago, when I got my first HS300. I used Kill A Watt model P4400, which is similar to yours but reports just one decimal instead of two. At that time I found that each plug turned on added 0.6W, and I did not detect the baseline usage at all. This result is a little different than yours, so I was inspired to repeat my measurements.

Instead of the Kill A Watt I used before, I decided to use a smart plug. @kevin1 found that they are precise to a very small fraction of a watt, see his post Data Science of "On", "Off" and "Standby": II - #5 by kevin1.

When I measured energy usage in this way, I found that instead of a static number, the value was constantly changing. I don’t remember my Kill A Watt jumping around like that. To dig a little deeper, I plotted the value over time. My measurement technique for recording from the Kasa app is described in the post Data Science of "On", "Off" and "Standby": II - #4 by jefflayman.
HS110 usage
The results above are one minute’s worth of data for the blue line, and a second minute’s worth for the orange line. The average of each series is also plotted as a horizontal dotted line. I could discern no pattern in the variability, but in general my result is near 1⅓ W while off and 2W while on. These values agree well with what you measured.
KP115 usage
I do not own a WeMo, so could not compare to your data there. I do have the KP115, so I repeated the above measurement on it. I watched it for a while in addition to these recorded measurements, and continued to see spikes well outside the general trend, so apparently the KP-115 just has more scatter. The good news is that the average energy usage is less than the HS110: I would call it 0.6W while off and 1.2W while on.
HS300 usage
Of course I also repeated the measurement on the HS300. Results are shown in the chart above, where the colored lines indicate how many plugs are turned on. Variability was much like the HS110, and averages were close to your measurements.

My HS300 hardware does have the USB sockets, so that may account for the slight variation present. I don’t know how to pull out the firmware version number, but the Kasa app reports “No Updates Available” so at least it is current. My HS110 is like yours in that it does not have a USB socket.


Nice charts. I can imagine with the very slow refresh of a Kill A Watt LCD screen, the sample rate may be a bit lower vs the smart plugs.
The numbers i provided were the average… there would typically be three readings on my Kill A Watt as the power would fluctuate… and I provided the middle number which i would see majority of the time.

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Just reading a little from the Kill-aWatt manual, it looks the like the Kill-A-Watt updates readings every second, but it might be the case that the power reading (Watts) is based on accumulated power (energy), rather than power for that second.

"1. The LCD shows all meter readings: Volts, Current, Watts, Frequency, Power Factor, and VA. The unit will start to accumulate KWH and powered duration time (hour) after power is applied. "

That the units are wifi, and polled, probably contributes a great deal to the variability of power consumption.

updated original post with KP115 and with HS300 status lights off in the Kasa app