DOCS II vs KD DFU
Price, ratings, monetisation and update history for both apps, side by side — with what reviewers say about each.
DOCS II
This app automates the capture and reporting of visible emission observations for air quality compliance. It uses location data, weather, and sun angles to document opacity levels, helping users avoid costly fines. The tool generates compliance archives for regulated sources.
- Automated Visible Emission Observation (VEO) capture
- Integration with Google Maps, compass, and inclinometers
- Real-time weather and sun angle data
- Opacity level documentation
- Automated VEO report generation
- Compliance archive creation
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DOCS II is developed by Virtual Technology, LLC, located in Rio Rico, Arizona. Air Quality has been driven by Opacity Emission standards since the 1800s, with Opacity percentages used to determine airflow requirements for various coal-fired boilers. Every locality in the USA has a standing Visible Emission Opacity limit of no more than 40% Opacity over any six minutes. Visible Emission Standards lowering this opacity limit to 20% / 5% / Zero are not uncommon in the USA, with enforcement of air pollution regulations at the federal, state, and local levels. Failure to adhere to these regulations is very costly, as violations of opacity limits can result in fines of $25,000 per source per day. The most common methods to monitor opacity levels are EPA Method 9, EPA Alternative Method 082, ASTM D7520-16, Digital Camera Opacity Technique, using EPA Method 22. The methods are a visible emission indicator of smoke or no smoke, followed by a Visible Emission Observation (VEO) to determine Opacity. A Visible Emissions Manager completely automates the entire capture of information needed for a Visible Emission Observation. Using Google Maps, compass, inclinometers, distance calculations, online weather, and sun angle data, the VEO is documented with populated data. With the local data captured, the VEO is uploaded to the Virtual Technology LLC servers, and a completed VEO report is generated to create the compliance archive. Nuisance ‘visible’ emissions accounted for over 85% of Air Quality complaints until today are still monitored exclusively by the highly subjective human observation method 9. Visible Emissions Manager is the solution for measuring Opacity and managing complaints of Nuisance Visible Emissions and regulated sources.
KD DFU
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A utility to do the door lock firmware upgrade
Screenshots
Verdict
The clearest difference is update cadence: KD DFU at every 2 months against DOCS II's every 58 months. KD DFU also leads on iOS requirement (12.0 vs 15.0). On price, ads, in-app purchases and device support there is nothing between them.
Scored on Price · Rating · Positive reviews · Number of ratings · Update frequency · Ads · In-app purchases · Monetization · Best chart rank · Devices · Requires iOS
Both are free to download. Neither carries in-app purchases, so what you see is what you pay.
DOCS II ships an update every 58 months, KD DFU every 2 months. The most recent releases landed on October 2, 2026 and September 26, 2026 respectively.
| Parameter | DOCS II | KD DFU |
|---|---|---|
| Price | Free | Free |
| Rating | 5.0 (1 ratings) — better | — |
| Number of ratings | 1 — better | — |
| Update frequency | Every 58 months | Every 2 months — better |
| Ads | No | No |
| In-app purchases | No | No |
| Monetization | Free | — |
| Devices | iPhone, iPad, iPod — better | iPhone, iPod |
| Requires iOS | 15.0 | 12.0 — better |
| Further details — not scored | ||
| Size | 91 MB | 26 MB |
| Age rating | 4+ | 4+ |
| Developer | Virtual Technology LLC | Guangzhou Kuodao Internet of Things Technology Co., Ltd. |
In-app purchases
DOCS II
No in-app purchases
KD DFU
No in-app purchases









