I think there's a saturated solution of sodium acetate inside. The metal clickie causes the solution to crystallize, which happens to happen exothermically.

(IANAchemist)

Can I use sodium acetate to heat my energy passive home (which I will build soon) by heating it at day in Trombe wall and discharging it at night?

It's most likely unwieldy. Sometimes you can cause the exothermic effect to occur without you wanting it by a vibration or shock.

Sodium Acetate.

https://en.wikipedia.org/wiki/Sodium_acetate

They are a supersaturated Sodium acetate solution. Liquids give off energy when they freeze and take energy in when they melt.

When you heat these and melt them they can stay stable as a saturated liquid until you create a small site for them to start freezing around - they then give off energy when they freeze. The 'clicker' is all that's required to localy concentrate it enough to form a single crystal seed to start the freezing