Alarms for deafblind people: when touch is the only channel
Short answer: When sight and hearing are both affected, touch is usually the channel you can depend on to be woken by, which in practice means a bed shaker or a worn vibration alarm rather than any clock built around a sound or a flashing light. Which of the two suits you depends on how much residual vision and hearing you have, whether you share a bed, and how much you move at night. No single device covers waking, checking the time, the door and fire alerting at once, and the most common expensive mistake is buying one thing and assuming it does all four.
Deafblindness is a range, not an absence
The word covers a very wide set of situations. Sense and Deafblind UK both use "deafblind" as a single word; a lot of services and assessments use "dual sensory loss" or "combined sight and hearing loss" instead, and people use different terms for themselves. Very few deafblind people have no vision and no hearing at all. Most have some of one, some of the other, or usable amounts of both in the right conditions.
That matters for buying decisions more than anything else on this page. Someone with Usher syndrome who has good central vision in daylight and a night-time field loss has a different problem from someone whose hearing has gone in their seventies on top of macular degeneration. Advice written as though deafblind means total is advice you should discount, and so is advice that assumes you can read a display in a dark room at 6am because you can read one under a lamp at noon.
The amount of light reaching your eyes also matters for something other than seeing. Where there is no light perception at all, the body clock loses the daily reset it normally gets from daylight and the sleep window can drift later day after day, which is non-24-hour sleep-wake rhythm disorder and a medical question rather than an alarm one.
Because of that range, the two single-sense guides are worth reading alongside this one rather than instead of it. Alarm clocks for deaf and hard-of-hearing people covers the equipment landscape when hearing is the affected sense, and alarms for blind and low-vision users covers the interface problems when sight is. If you have usable hearing in quiet conditions, or usable vision in good light, the options on those pages may still be open to you and this page would otherwise close them off unnecessarily.
Two other things change the picture at night specifically. Hearing aids and cochlear implant processors normally come out before sleep, which removes whatever hearing you rely on during the day. And your eyes are unaided in the same way if your usable vision depends on magnification, lighting or contrast. Waking up when your hearing aids are out overnight covers that gap on its own terms.
Why vibration is usually what is left
An audible alarm has to cross a hearing loss and then reach a brain that is asleep, without the aid that makes daytime hearing work. A flashing alarm has to cross a sight loss and then reach a visual system through closed eyelids. Vibration goes through skin, which is not switched off, does not need an aid in, and does not care whether the room is dark.
It is worth being precise about what that does and does not mean. A vibration alarm is a different sensory channel, not a stronger one. Whether any given stimulus wakes any given person on any given night depends on sleep stage, sleep debt, age, alcohol, medication and a good deal else, and nobody can promise you an arousal. What vibration removes is the specific failure of sending a signal down a route that is impaired. That is a real advantage and it is a narrower claim than most product pages make. Vibration alarms compared with sound alarms goes into the general case.
Bed shaker or worn device, when there is no backup channel
For a hearing reader, a wrist band that gets slept through is annoying because the phone alarm across the room still catches them. For a deafblind reader there is no second channel underneath. That single fact should shape the decision.
A bed shaker is a puck or pad that sits under the pillow or under the mattress, driven by a mains-powered bedside clock. It moves a large object rather than one patch of skin, and it does not depend on where your arm ends up during the night. Under the pillow is generally the more forceful placement and the one people notice most; under the mattress spreads the movement out and is less likely to be shrugged off but also less concentrated. It is the stronger option for most people and it is the usual first recommendation from sensory services.
A worn vibration alarm reaches only the person wearing it, travels, and works in a chair, a hospital bed or a sofa where there is no mattress to shake. It is the better answer in a shared bed, because a mattress shaker wakes both of you. Against that, a band can rotate on the wrist, can be taken off half-asleep, and needs charging on a schedule you have to remember.
Bed shaker versus wrist-worn vibration alarm sets the two against each other properly. The specific recommendation for combined sight and hearing loss is redundancy: if the consequences of not waking are serious, run both, on the same schedule, rather than trusting either alone.
Tactile clocks and knowing what time it is
Waking up and knowing the time are separate problems, and only the first is solved by an alarm.
A tactile watch or clock has a hinged cover you lift to feel the hands against raised markers. A braille clock presents the time as dots. Some tactile watches signal the time through vibration patterns rather than a face. All of these let you check the time silently and without light, which is exactly what is needed if a spoken announcement is no use to you and a lit display is no use either.
Two honest caveats. Braille is not a universal skill, and most people who lose sight do so later in life and never read it fluently. If you do not read braille comfortably, a tactile analogue face is the more practical route and there is nothing second-rate about that. And a tactile timepiece is a timepiece. It tells you the time when you ask; it does not wake you.