Independent comparisons. We may earn from shop links. More info

How to use a socket tester

Updated: 22 October 2026

You are holding a BS 1363 plug with lamps or a screen, and it is tempting to push it into a socket you have just wired and treat a glow as the finished job. Learning how to use a socket tester is mostly the order of the checks, and the point where you stop. Prove the tester on a live socket you already trust, read only the legend on that model, and treat anything else as a reason to leave the faceplate on. This sits beside our [socket tester comparison](/hub/measuring-equipment/socket-tester). The page is from the Products Compared editorial team, updated on 21 October 2026. A qualifying purchase can earn us a commission at no extra cost to you.

You are holding a BS 1363 plug with lamps or a screen, and it is tempting to push it into a socket you have just wired and treat a glow as the finished job.

Our top picks

Martindale Martindale BZ101 Buzz-It

Best overall

Martindale Martindale BZ101 Buzz-It
8.4/10about £17.34
View offer
Kewtech Kewtech KEWCHECK 103

Alternative

Kewtech Kewtech KEWCHECK 103
8.0/10about £22.00
View offer
KAIWEETS KAIWEETS HT106E

Best value

KAIWEETS KAIWEETS HT106E
6.9/10about £11.99
View offer
On this page
  1. 1.Before you plug it into the suspect socket
  2. 2.Plug in and read
  3. 3.Using the tone as a fuse finder
  4. 4.When you stop and call someone

Before you plug it into the suspect socket

Look for a crack, a bent pin, or a legend you cannot read. A photo of another brand will not interpret a smeared chart. The KEWCHECK 103 treats three green LEDs and a continuous tone as its pass. The BZ101 uses its own front label. Martindale tells check-plug users to verify on a known good live socket before and after the suspect one. If that socket stays dark, the tester, the switch, or the circuit may be the cause. Move on only when the known socket shows the pass.

Plug in and read

Switch the suspect socket on. With the switch off, or the MCB off, no lamps means no supply detected, not wiring correct. Seat the plug fully, then read the legend on that plug. On the KEWCHECK 103, three greens and a steady tone are the pass, and a warble is a fault. Do not copy those three greens onto another brand. If the pattern is anything else, stop, and do not swap brown and blue from a diagram. What the words point at is on the socket tester lights meaning page. A correct pattern on an extension lead does not certify the reel or the earth path.
Martindale Martindale BZ101 Buzz-It

Testsieger

Martindale Martindale BZ101 Buzz-It
8.4/10about £17.34
View offer

Using the tone as a fuse finder

Only a plug that sounds can find a fuse. The BZ101 listing says the buzzer stops when the correct fuse is pulled. Pull one device at a time and push it back before the next. A ring, an RCBO or a shared neutral means that device is a clue, not a full diagram. If you cannot hear the tone, fetch a second person. The HT106E and the HT107E have no buzzer, and the Proster pen is not a fuse finder for the outlet. Do not press an RCD button while you hunt a fuse. That check is on the socket tester RCD test page.

When you stop and call someone

Stop when the pattern is not the pass, when you feel a tingle, when an RCD will not reset, or when the job is new work. Best Practice Guide 8 says you do not energise a new, repositioned or replaced socket and then use a plug as the verification. That sits under BS 7671. Live and earth reversed, heat, a burning smell, or a plug that will not seat is a stop. None of these plugs measures loop impedance. If the pass appears and you still do not trust the socket, that matches the HSE note that a tester can indicate safe when the socket is not.

Common questions

Do I switch the socket off before I plug the tester in?
Switch it on to test it. The indication comes from the supply. Off, or isolated at the board, a blank tester is expected and it says nothing about line, neutral and earth. You can insert the plug with the switch off and then switch on. Do not leave the switch off and call the darkness a pass.
What if nothing lights?
No lights can mean the socket is off, the circuit is dead, the plug is not seated, or the tester has failed. Prove the same tester on a known live socket before you decide the suspect outlet has no supply. On the HT106E, a dead socket produces no wiring report. Darkness is not a code for correct.
How do I know the tester itself works?
Use a socket you already trust and that you know is live, and look for that model's pass. Martindale's check-plug guidance is to do this before and after the suspect socket. If the known socket will not light the tester, stop and sort the tester or that circuit before you condemn every other outlet.
Can I use the buzzer to find the MCB on my own?
Yes, if you can hear the BZ101 or the KEWCHECK 103 from the consumer unit. Pull one device at a time until the tone stops, then restore the others. If the tone is too quiet, or the Kewtech beep is painful, get a helper. A silent LCD will not name the device from the board.
Is a correct pattern enough after I changed a socket?
No. Best Practice Guide 8 treats a plug-in tester as the wrong verification for a new, moved or replaced socket. The pass only means that model's legend matched on a live supply. Earth-loop impedance, supply polarity and insulation sit outside these plugs. A competent person verifies that work under BS 7671.
Can I leave it plugged in?
You can, and reviewers do, including as a rough check that a socket is live. It is also easy to walk away and lose, which shows up in BZ101 reviews as a lost tool. It is not watching the earth path while you are out. Unplug it when the check is done.
Does this work on an extension lead the same way?
Yes, with the same limits. A pass at the lead means the legend was satisfied at those pins, not that the reel or the earth is sound. If the wall socket passes and the lead does not, you have a clue about the lead. You still should not open a moulded plug and swap conductors from a generic chart.

Related pages

Socket tester buying guide

Socket tester

Best socket tester UK: a published limit, not stars

Socket tester RCD test: a trip is not a timed result

Socket tester lights meaning: use this legend only

Sources

Public UK sources from the research digest, last checked on 21 October 2026. Shelf prices and star lines are the amazon.co.uk figures captured with these eleven listings. The price bands are this set, not a market average.

  1. Electrical Safety First, Best Practice Guide 8, Issue 2 (February 2015) (retrieved 21 October 2026)
  2. HSE: electricity FAQ (retrieved 21 October 2026)
  3. ESQCR 2002, regulation 27 (retrieved 21 October 2026)
  4. SP Energy Networks: voltage changes (retrieved 21 October 2026)
  5. Martindale BZ101 data sheet (retrieved 21 October 2026)
  6. Kewtech KEWCHECK 103 (retrieved 21 October 2026)
  7. BEAMA RCD handbook 2018 (retrieved 21 October 2026)
  8. amazon.co.uk, Martindale BZ101 listing (retrieved 21 October 2026)