I hope McDermot's non functioning transmitter has a drop off mechanism because it would a shame for him to carry that around the rest of his life. I know they make them so they do fall off when they are no more use to the research project. 
Unwaxed dental floss is used to fit the transmitter packpacks - an individualized fit for each bird. The floss usually degrades in about two years and then the transmitters drop off. The floss is used at the front of the backpack and on the back - when one of the location degrades the bird can shake the pack off quite easily - it's build to slide off once one of the floss points degrades. An earlier backpack configuration used to break or degrade and it used to leave the transmitter hanging around the birds's necks, wasn't used for long needless to say. If the transmitter is still operational when it drops off, researchers will have a couple of days maybe to find it and retrieve it before the battery loses power and the signal is lost - that's assuming it isnt' run over or crushed in the meantime. If it isn't operational, then it would be just luck if anyone found it in time to be returned to the researchers. Researchers buy the transmitters for thousands of dollars each knowing that most will not be retrieved but it's a fair tradeoff - limited time on the bird and the hope that the data retrieved will prove useful, particularly since most transmitters projects are on species at risk or about which we know very little. Generally can't get organizations/agencies to fund expensive transmitter research (thousands for equipment, thousands more for satellite time) on species we do know alot about or that are quite common. Generally that it, know that there have been satellite transmitters put on cats, but then how much do we know about Fluffy, other than he he seems very dignified, likes occasional to bring "presents" home and he considers humans as "staff".
There are some quick release mechanisms for transmitters but my understanding is that they aren't commonly used on birds, or at least not on peregrines, because of the risk that the mechanism will become caught on a branch, nest, during mating, hunting, when being attacked, etc. Over the centuries falconers have learned that anything on a hunting raptor needs to be able to slide through things like branches, stay out of the way of hunting and flying, etc and that if a bird does decide to resume its wild life, it's falconry acoutrements, which are most often made of leather, eventually either rot off or can be chewed off in a relatively quick order if the bird so desires. (Heck birds manage to get aluminium bands off occasionally!) The individualized fit and the use of the dental floss helps to keep the transmitters on securely enough to keep the bird safe but not indefinitely or so securely that when part of the floss degrades (or is cut) that the whole unit can't be wriggled out of easily enough by the peregrine. As the unit is fitted, there are finger widths of space at various points - it keeps the backpack in the proper location without it shifting and interfering with the bird's normal activities. For folks who have knapsacks with the breast strap across the front - the idea isn't to have it tight, just the right length to keep the pack from cutting over and under the arms or from interfering from natural movement at the same time that it keeps a heavy pack in the right place so as not to cause damage to the person wearing it. If your pack is fitted correctly, then nothing is tight or binds and the whole pack can shift but only within a prescribed range and the weight is properly/evenly distributed and secure (ie: going over your head if you have to bend down/over or fall). Until you unclip the breast strap that is, at which point the pack slips off your arms easily - if fitted correctly. Principle is the same for the transmitter backpacks but instead of a clip which is hazardous, you have biodegradable dental floss.
