The Smell Is Not An Exaggeration

If you take one thing away from this review, take this: the smell is the defining feature of the Zero In Outdoor Fly Trap, and reviewers are unanimous about it even when they love the product. One 3-star buyer says: "Absolutely works to catch flies... probably one of the worst smells I have ever come across! You can also smell it when in close proximity to it so not ideal to be used near to outdoor areas where you're likely to spend time."

Another 3-star reviewer goes further: "the smell is so bad, it's hard to describe how actually bad it is until you see for yourself, imagine a dead animal at your back door and then multiply that by 5."

This is the bait doing exactly what the bait is meant to do. It is a fermenting attractant designed to mimic something flies want to lay eggs on, and once the trap fills up with dead flies, it gets worse. Several reviewers describe maggots inside the bottle within a couple of weeks. One 4-star buyer notes: "the trapped ones were laying eggs so they got full of maggots creating even more flies."

This means placement is non-negotiable. You cannot hang one of these next to your patio chairs, next to a back door you keep open, or anywhere near a window. Reviewers who hang them at the bottom of the garden, near the bins, near a kennel, or behind a hedge are the ones writing 5-star reviews. Reviewers who hang them on the patio are the ones giving up on the product after a week.

Does It Attract More Flies Than It Kills?

This is the second-biggest debate in the reviews, and it is more split than the smell question. Some buyers are convinced the trap pulls flies in from neighbouring properties faster than it can kill them, especially in the first day or two before the catch volume catches up.

One 4-star reviewer puts it well: "It seems to attract flies from everywhere! I feel like I actually noticed more flies around at first, but thankfully they all ended up on the trap pretty quickly." A 1-star buyer used one in a conservatory near pet food bowls and reports a much worse outcome: "the flies absolutely LOVE it and there were hundreds swarming around constantly, led to horrific infestation and egg laying would absolutely not use again."

The pattern in the reviews is fairly clear once you stack them up. Outdoors, far from the house, the trap solves the problem because the catch rate beats the attract rate within 24 to 48 hours. Indoors or right next to where you live, you can end up with a localised swarm before the trap takes over. The product description says outdoor only, and the reviews back that up sharply, this is not a use-it-anywhere bit of pest kit.

One 5-star buyer who lives near horse fields gives the cleanest summary of the success case: "I set up one of these traps at the bottom of the garden, it was that full within three weeks, I had to add more water, as the flies were just standing on bodies of their drowned buddies. There are literally 100s in each trap."

The Setup Reviewers Get Wrong

The instructions are simple on paper. Empty the bait sachet into the bottle, add 300ml of water, hang in sunlight, wait. In practice, two things trip people up.

First, the lid design. Zero In has shipped at least two versions of the bottle, and reviewers have hit problems with both. One 2-star buyer notes: "The lid design has clearly changed and the instructions on the bottle packaging haven't been updated because it still says to screw open the lid." If you are getting one of the newer twin packs, the instruction image on the listing is the source of truth, not the bottle label. Old version: lift the lid and lock it open before adding the sachet. New version: remove the lid, add sachet, add water, replace lid. If you mix them up the trap leaks or the seal fails.

Second, sun and patience. Multiple 5-star reviewers stress the same point. One says: "It says it activates 24 hrs after mixing however, within a couple of hours it caught its first 8 flies." Another with two pairs of traps gives placement coordinates: "Position somewhere outside that catches the sun. We have 2 facing east & 2 west." A few 1-star reviews complain about no flies after three days, and reading between the lines, those traps are usually somewhere shaded or wind-exposed. The bait needs warmth and still air to volatilise enough to pull flies in.

Where Twin Packs Actually Get Used

Looking at where buyers say they hang these tells you more about the product than any spec sheet would. The use cases that come up repeatedly:

Around bins and food waste. The product description names this directly, and reviewers back it up. If you have a wheelie bin that gets a swarm in July, hanging one trap on a fence post a couple of metres from the bin is the textbook use case.

Near dog and chicken areas. One 5-star buyer explains: "Great for keeping flys away from dog bowls also etc." Another buyer in the country writes about horse-field flies. Anyone with kennels or a chicken run will already know how bad the fly load can get, and these traps are sized for exactly that scenario.

By back doors, but at a distance. Several reviewers describe putting one trap a fair way from the back door to intercept flies before they reach the house. One says: "hang bottom of the garden keep flies away. Work really good." Another: "I put mine by the back door summer time hardly any fly's get indoors."

BBQ season. The summer BBQ use case is the most common reason buyers come back. Multiple 5-star reviews say they buy these every summer and run two to four at a time, exactly what the twin pack is sized for. Hang one on each side of the garden so the flies head for the bottle rather than your plate.

The Quality Drift Reviewers Are Worried About

This is the part of the review pattern that should give returning buyers a slight pause. A small but consistent thread of recent 1-star and 2-star reviews comes from people who have used Zero In traps for years and feel the latest batches are weaker.

One subscriber writes: "The original version was fantastic and it filled up so quickly. We created a subscription for them and have used for a couple years now. Unfortunately they have recently changed the design of the containers and they don't stay up right, the liquid doesn't mix as well, and they are now ineffective." A 2-star buyer says simply: "plastic straps instead of shoe lace type ones. Was even missing one." A 1-star reviewer writes: "This batch is awful they are not attracting any flies."

Stacked against thousands of glowing reviews, this is a minority complaint, but it is recent, repeated, and specific (lid changes, weaker bait, plastic straps, missing pieces). If you are buying these for the first time, it is unlikely to land you in the dud-batch group. If you have been a happy buyer for years and the latest pack feels different, you are not imagining it.

Disposal: The Bit Nobody Plans For

You hang the trap, it fills up, then what? This is where the smell question comes back with a vengeance. The product instructions say to bury the contents or dispose in a plastic bag with household refuse. Reviewers who actually do this universally describe it as horrible.

One 3-star buyer says: "After emptying and refilling once I don't think I will be reusing them, and will dispose once finished because the smell is absolutely disgusting." Another 5-star reviewer offers a workaround that several buyers second: "I clean them by emptying the contents into a dog poo bag and dispose in the normal household bin." A 5-star buyer warns about the worms: "Once finished dispose as you will see worms in the container."

Practical takeaway: at £6 for a twin pack, plenty of buyers treat the bottles as effectively single-use. You can buy refill bait sachets (Zero In code STV337, sold separately) if you want to keep going, but you do not have to feel bad about binning the lot at the end of the season. The economics still work.

Final Verdict And Who It Actually Suits

For £6, you get two reusable bottle traps, two ready-to-use bait sachets, and roughly four to six weeks of summer fly control if you set them up properly. The Amazon score of 4.4 across 21,461 ratings reflects what the reviews show: most buyers, used to it as an outdoor garden product, are very happy.

This pack is right for you if:

• You have a UK garden with a fly problem in summer, especially near bins, compost, dogs, chickens, or livestock.
• You can hang the trap at the bottom of the garden or behind a fence, well away from where you sit and well away from open windows.
• You are happy to dispose of a smelly bottle of dead flies and worms at the end of the season.
• You want a non-toxic option that does not involve sprays or sticky strips around children and pets.

This pack is wrong for you if:

• You want something for indoors, a conservatory, or a covered patio. Other reviewers learned the hard way that the trap pulls flies in faster than it catches them in enclosed spaces.
• Your garden is small enough that there is nowhere to put the trap five or six metres away from where you sit.
• You cannot deal with the smell at empty time. Sticky tape strips are less effective but smell-free.

For the right garden, the right placement and a tolerance for what happens inside the bottle, this is one of the most cost-effective summer fly fixes on Amazon UK at the moment. For the wrong setup, it will create more problems than it solves. Match yourself to the use case before you click buy.