The best Christmas light testers, and what each one cannot fix
Half a string goes dark because one bulb failed in a series circuit. The right tool finds it in a minute — if it works on your kind of light.
By Sawyer V. · Published
A string of mini lights with one dark section is the most common Christmas lighting fault, and the one most often solved by throwing the string away. A repair tool finds or bypasses the bad bulb in a minute and saves the set — and on a pre-lit tree, it saves the tree.
The tools are specific about what they can fix, which is the most useful thing about them. Five below.
Wreath & Watt earns a commission on qualifying purchases made through the Amazon links on this page. It costs you nothing and it does not change the order of the picks — here is exactly how we are funded.
Quick picks
| # | Product | Best for | Score | Price |
|---|---|---|---|---|
| 1 |  Light Keeper Pro, incandescent mini light repair toolPulses the set to fix failed shunts, plus bulb and fuse testers | Incandescent mini lights and pre-lit trees | 7.8/ 10 | $37.90Amazon #ad · Price as of October 26, 2026 · Disclosure |
| 2 |  LightKeeper Pro and LED Keeper Pro combo packBoth repair tools in one pack | LED strings, and incandescent ones in the same box | 6.5/ 10 | |
| 3 |  Weikani non-contact voltage tester pen, 60-1000 V AC60-1000 V AC, non-contact, works on any string | Finding the dead section on either type | 6.8/ 10 | $8.99Amazon #ad · Price as of October 26, 2026 · Disclosure |
| 4 |  HLS TEST-200 mini light tester and repair gunMini light tester and repair gun | A second tool for the other hand | 4.8/ 10 | $34.18Amazon #ad · Price as of October 26, 2026 · Disclosure |
| 5 |  Light Keeper light fixing toolThe listing publishes nothing beyond the nameSkip this | Skip | 1.3/ 10 | $27.43Amazon #ad · Price as of October 26, 2026 · Disclosure |
Scores are our own weighting of published manufacturer specifications, explained in full on how we research. They are not test results. We have not tested these products.
The picks in full
#1 — Incandescent mini lights and pre-lit trees
Light Keeper Pro, incandescent mini light repair tool
Pulses the set to fix failed shunts, plus bulb and fuse testers
7.8
/ 10
The pick for incandescent strings and older pre-lit trees. The limitations list is honest; read it before you buy.
Published specifications
- Works on
- Incandescent mini light sets, including icicle, net, pre-lit trees and wreaths
- Method
- Plug into an empty socket, pull the trigger to fix the shunt
- Also includes
- Audible continuity detector, bulb tester, fuse tester, bulb puller, storage compartment
- Spare bulbs
- 2.5 V, 170 mA
- Does not work on
- LEDs, control-box sets, rope lights, battery sets
- Voltage
- 120 V only
Our scoring
- Fixes the common fault
- 10 / 10
- Published limitations
- 10 / 10
- LED support
- 1 / 10
- Spec completeness
- 10 / 10
Good
- Fixes the most common failure — a bulb whose shunt did not close — without finding the bulb first
- Publishes exactly what it cannot fix, which is rare and useful
Watch out
- Incandescent only; it does nothing for LED strings
- No help with sets on a control box
#ad · Price as of October 26, 2026 · How we are funded
Specs from the Amazon listing (ASIN B002DGM9V2), verified 2026-09-11.
#2 — LED strings, and incandescent ones in the same box
LightKeeper Pro and LED Keeper Pro combo pack
Both repair tools in one pack
6.5
/ 10
The pick if you own both incandescent and LED strings. Buy the single tool above instead if all your sets are one kind.
Published specifications
- Contents
- LightKeeper Pro and LED Keeper Pro
- Works on
- LED light sets and incandescent mini light sets
- Exclusions
- Not stated in the listing
Our scoring
- LED support
- 10 / 10
- Published limitations
- 2 / 10
- Accessories
- 9 / 10
- Spec completeness
- 5 / 10
Good
- The only listing that still carries the LED Keeper Pro, and it brings the incandescent tool with it — if you own both kinds of string, this is one purchase instead of two
- Covers the two failure modes on this page in one box: a failed shunt on an incandescent set and a dead section on an LED set
Watch out
- It contains the Light Keeper Pro, which is our pick above — if you already own that tool you are buying it twice
- This listing publishes no exclusions, where the standalone LED Keeper Pro listing used to state that it will not fix parallel-wired sets, control-box sets or thin micro-wired LEDs; those limits still apply to the tool, and you should check your string's construction before relying on it
- The highest price on this page, because it is two tools
Contents from the Amazon listing (ASIN B0DPXP98WF), verified via the Creators API 2026-10-07. Replaces B0D5MXVM91, the standalone LED Keeper Pro, which Amazon no longer returns. The LED Keeper Pro itself is unchanged — this is the live listing that carries it — but the published exclusion list that came with the standalone listing is not on this one, so the entry no longer presents those limits as published and says so in the cons instead.
#3 — Finding the dead section on either type
Weikani non-contact voltage tester pen, 60-1000 V AC
60-1000 V AC, non-contact, works on any string
6.8
/ 10
Buy it to find where a string goes dead, whichever type it is. It fixes nothing — pair it with the Light Keeper Pro for incandescent or the LED Keeper for LED.
Published specifications
- Works on
- Any mains AC light string — LED or incandescent
- Range
- 60 to 1000 V AC
- Detection
- Non-contact — the tip glows red and the buzzer beeps
- Safety marks
- CAT IV, ETL, CE
- Extras
- LED flashlight, pocket clip, ABS case
- Repair
- Not stated in the listing
Our scoring
- LED and incandescent
- 10 / 10
- Repair function
- 1 / 10
- Published detail
- 8 / 10
- Spec completeness
- 8 / 10
Good
- It reads voltage in the cord rather than testing a bulb, so it works on LED and incandescent strings alike — the repair tools here each work on one
- CAT IV with ETL and CE marks published, which no other tool on this page publishes
- Non-contact, so there is no socket to open or bulb to pull to find where the run goes dead
- A flashlight in the same pen, which is the other thing you want on a roof in December
Watch out
- A detector, not a repair tool — it finds where the voltage stops; you still replace the bulb or the fuse
- It narrows the fault to a section, not to the individual dead bulb
- It starts at 60 V, so it is no help on a battery-powered string
#ad · Price as of October 26, 2026 · How we are funded
Specs from the Amazon listing (ASIN B0C5X9W86Q), verified via the Creators API 2026-10-06. Replaces B083752K35, which Amazon now shows as currently unavailable. No live tool tests both LED and incandescent bulbs directly — the Lightkeeper Pro listing explicitly excludes LEDs and the LED Keeper is LED-only, and both are already on this page — so the slot now carries a non-contact AC voltage pen, which works on either type because it reads the cord rather than the bulb. The slot has been retitled from finding the dead bulb to finding the dead section.
#4 — A second tool for the other hand
HLS TEST-200 mini light tester and repair gun
Mini light tester and repair gun
4.8
/ 10
A reasonable alternative to the Light Keeper Pro for incandescent minis. The Light Keeper publishes more.
Published specifications
- Format
- Tester and repair gun
- Works on
- Mini lights
- LED support
- Not stated in the listing
Our scoring
- Function
- 8 / 10
- LED support
- 2 / 10
- Published detail
- 4 / 10
- Spec completeness
- 5 / 10
Good
- A tester and repair gun in one, from a holiday lighting supplier
Watch out
- LED support not stated
- Little else published
#ad · Price as of October 26, 2026 · How we are funded
Specs from the Amazon listing (ASIN B003YO273M), verified 2026-09-11.
#5 — skip this
Light Keeper light fixing tool
The listing publishes nothing beyond the name
1.3
/ 10
Our skip. On a page where LED-versus-incandescent compatibility is the whole question, this listing will not answer it. Buy the Pro that names your string type.
Published specifications
- Works on
- Not stated in the listing
- Limitations
- Not stated in the listing
- In the box
- Not stated in the listing
Our scoring
- LED support
- 2 / 10
- Published limitations
- 1 / 10
- Published detail
- 1 / 10
- Spec completeness
- 1 / 10
Good
- A Light Keeper tool, from the family that makes the two picks above it
Watch out
- The listing does not say whether it fixes LED or incandescent strings, which is the one thing that decides whether it is any use to you
- Nothing published about the contents or the exclusions
#ad · Price as of October 26, 2026 · How we are funded
Specs from the Amazon listing (ASIN B00QVBIG30), verified via the Creators API 2026-09-24. Replaces the discontinued LED Light Keeper (B009SDS6QK).
How we ranked these
Published compatibility and limitations first, then function — repair, or test only.
| Tool | Incandescent | LED | Repairs | Limitations published |
|---|---|---|---|---|
| Light Keeper Pro | Yes | No | Yes, plus testers | Yes |
| LED Keeper Pro combo | Not stated | Yes | Yes | Yes |
| Weikani voltage pen | Yes | Yes | Detect only | No |
| HLS TEST-200 | Yes | Not stated | Yes | No |
| Light Keeper fixing tool | Not stated | Not stated | Not stated | No |
Two tools publish what they cannot fix. That list is the most useful spec in the category; our skip publishes nothing at all.
Source: Manufacturer listings on Amazon.com, verified September 2026.
Why one bulb darkens a section
The arithmetic
- Light Keeper Pro spare bulbs: 2.5 V each, published
- 120 V household supply / 2.5 V = 48
- So about 50 bulbs share one series circuit
An incandescent mini string is wired in series sections of about 50 bulbs. When one bulb fails and its internal shunt does not close, the whole section goes dark — which is exactly the fault these tools are built to find.
The full diagnostic sequence, from fuses to connectors, is on Christmas light troubleshooting.
For incandescent strings and pre-lit trees
The Light Keeper Pro plugs into an empty socket and sends a pulse through the section that closes the failed shunt, so the rest of the section lights and the dead bulb shows itself. It also carries a bulb tester, a fuse tester, a continuity detector and a bulb puller. It publishes that it works on icicle and net lights and on pre-lit trees and wreaths — and that it does not work on LEDs, control-box sets, rope lights or battery sets.
For LED strings
Most strings bought in the last decade are LED, and the LED Keeper Pro is the tool for them, now bundled with the incandescent tool rather than sold on its own. If you own both kinds and mostly need to find where a run goes dead rather than bypass a bulb, the Weikani voltage pen covers both, because it reads the cord rather than the bulb — it detects, it does not repair.
What the tool tells you to buy
A tester finds the fault; it does not fix it. What it sends you to buy is a bulb, a fuse, or a new set — and the first two cost pennies. The replacement bulbs matched by base and color temperature, and the plug fuse to check before anything else when a whole string is dark, are on Christmas light replacement bulbs and fuses.
Saving a pre-lit tree
A pre-lit tree with a dark section is the most expensive thing these tools save. An incandescent pre-lit tree is the Light Keeper Pro’s best use; for LED pre-lit trees, check the exclusions before relying on the LED tool. How long pre-lit lights last in the first place is on how long Christmas lights last, and the pre-lit trade-off on pre-lit vs unlit.
Questions
›Why is half my string of lights out?
Mini strings are wired in series sections of about 50 bulbs. One bulb whose shunt did not close darkens its whole section. A repair tool finds or bypasses it.
›Does the Light Keeper Pro work on LED lights?
No. It publishes that it works on incandescent mini sets and does not work on LEDs, control-box sets, rope lights or battery sets. There is a separate LED tool.
›Can a light tester fix a pre-lit tree?
The Light Keeper Pro publishes that it works on pre-lit trees and wreaths with incandescent mini lights. For LED pre-lit trees, check the LED tool’s exclusions.
›Tester or repair tool?
A tester finds the dead bulb; a repair tool also bypasses the failed shunt so the section lights. One tool here only tests, but works on both LED and incandescent.
Sources
- Light Keeper Pro listing (ASIN B002DGM9V2) — Incandescent mini sets incl. pre-lit trees; shunt repair, bulb and fuse tester, continuity detector, bulb puller; 2.5 V 170 mA spares; not for LEDs, control boxes, rope or battery sets; 120 V
- LightKeeper Pro and LED Keeper Pro combo pack listing (ASIN B0DPXP98WF) — Both repair tools in one pack; no exclusions published on this listing
- Weikani non-contact voltage tester listing (ASIN B0C5X9W86Q) — Non-contact AC voltage detector pen, 60 to 1000 V, tip glows red with a buzzer, CAT IV, ETL and CE, LED flashlight, ABS case
- HLS TEST-200 listing (ASIN B003YO273M) — Mini light tester and repair gun
- Light Keeper light fixing tool listing (ASIN B00QVBIG30) — no light type, contents or exclusions published
- Series-circuit arithmetic — 120 V divided by the published 2.5 V spare bulb rating — our arithmetic
We have not tested these products. Every figure above comes from a published manufacturer specification or from arithmetic shown on this page, and anything a maker does not publish is printed as unavailable rather than estimated. How that works, and what we will not claim, is set out on how we research.