The idea behind the PSK™ is very simple - a detachable piece of plastic with keys in it (the key module) placed on 4 pressing force detectors located in the phone's housing, what allows to precisely determine on which key the pressing is applied, so no electronics is needed in the key module, thus the changeable key modules with divers layouts can be very cheap (cheaper than changeable faceplates). General view of the PSK™ in one of its numerous embodiments is shown on the figure below.

The key module can comprise movable buttons like those of the standard mobile phone keypad, as well as depicted keys which are activated by sufficient pressure on the corresponding regions of the key module's surface.

Some of the PSK™ advantages are listed below:

1. a number of versatile detachable key modules available for same cell phone/PDA, the key modules can have different number of buttons; the buttons positioning, their form, and their functions can differ as well (especially attractive for "young and fun" market);

2. interchangeable key modules are very cheap, no electronic components in the key modules (one of possible applications is disposable key modules for medical equipment);

3. no conductor matrix, so valuable real estate is saved (ultra thin devices, or more space for a battery);

4. the key modules can support arbitrary pointing operations, so navigation buttons can be eliminated, thus providing more valuable space for the mobile phone's display (this can also be used in mission critical applications where finger movements could be more reliable than finding buttons on the keypad);

5. movable buttons in the key module can be of any imaginable shape, e.g. stars, animals, symbols, etc., what can be hugely attractive to the young audience;

6. the key modules can be transparent (especially attractive for "young and fun" market);

7. changeable graphics can be added to the transparent key modules (especially attractive for "young and fun" market);

8. some key modules can be rotated with 90 degrees step angle, image on the phone's display rotates automatically to fit orientation of the keys in the key module;

9. sensitivity of the keys, i.e. the threshold of their activation, can be s/w adjusted (further personalization of the phone/PDA);

10. the key module can be changed in seconds (mission critical applications);

11. application specific design of the key modules is available (young and fun plus business applications);

12. multi-directional text input (like the MIK™) is available as an option (wide range of applications, but young and fun especially);

13. some biometric functions can be supported;

14. depressing with non-human pressing dynamics can be ignored, so no need to lock/unlock the keypad (mission critical applications);

15. the key module can be done of light metal (alloy) to increase durability in harsh conditions (mission critical applications);

16. easy check and high reliability, if at least one of the keys is working, then the rest of the keys are working as well (mission critical applications);

17. the keypad remains fully operational even if some of the keys are broken (mission critical applications);

18. the key module can be completely isolated from electronic circuit of the keypad for purpose of impermeability (mission critical applications);

19. low EMI radiation since there is no conductor matrix, no switches, no contact chatter;

20. touch (i.e. low pressure) can be detected before a key is actuated (i.e. sufficient pressure applied), so on touch graphical and voice promptings can be used to minimize error rate, the voice prompting could be used for blind people: when touching a key a "voice message" informs which of the keys to be actuated or what options are available through the key; graphical prompting can also be helpful when using multi-directional text input (like the MIK™) for input of characters of different languages (including oriental languages).

The electronic circuit of the PSK™ uses common cheap components and isn't expensive, or by other words, not considerably more expensive than those of the dome keypads. More, one electronic circuit and, let's say, 5 interchangeable key modules could be noticeably cheaper than five faceplates or five common keypads, here is an economy. 

As for the key module's layout data, RFID technology can optionally be used to inform mobile device about layout of the key module.

The PSK™ can also provide a lot of opportunities for the aftermarket manufacturers who could offer literally hundreds versions of the key modules (including very expensive ones) for any imaginable Customer.