Stix,
That looks like an interesting product - would be very interested to know if anyone has tried it and their feelings on it's usefullness (or otherwise). Found this info on the web but it is obviously the advertising blurb.....
Seachem Ammonia Alert
Description
Ammonia Alert continually monitors the level of ammonia in your tank. Tell at a glance if the level is safe, alert, alarm or toxic for your aquarium inhabitants. Reliable monitor lasts more than a year, giving round-the-clock readings of the number one fish killer in marine or freshwater tanks.
The unit consists of a waterproof reference color card and a replaceable sensor film. The detecting film, located in the center of the reference scale, changes reversibly from yellow to green to blue relative to the ammonia concentration. A convenient suction cup is included.
No test kits, chemicals, or procedures are needed.
Technical Information
Directions
Just place the unit visibly anywhere in the aquarium or filter. In the absence of free ammonia the unit will assume a yellow or faint yellow-green color. It is normal for the dry sensor to have a greenish hue. It may take up to a few days for a dry sensor to equilibrate with the water. No sampling of water, chemicals or test procedures are required. The presence of the free ammonia is detectable continuously with a response time of about 15 minutes. Response to decreasing ammonia is slower, requiring about four hours to go from toxic to safe on removal of ammonia.
Interpretation: As little as 0.02 mg/liter of free ammonia will produce a greenish hue on the detector surface. This corresponds to a total ammonia of 0.25 mg/liter in marine water at pH 8.3. In freshwater at pH at pH 7.0, this corresponds to 3.6 mg/liter as total ammonia. Free ammonia is much more toxic than ionized ammonia. As free ammonia, the alert color corresponds to about 0.05 mg/liter; alarm to about 0.2 mg/liter; toxic to about 0.5 mg/liter. The alert concentration is tolerated for several days; alarm for a few days; and toxic is rapidly harmful.
This product is not recommended for use at acid pH.