Short answer. Not exactly notice specifically, but you do need to manifest intent. Article 1534 says the transfer of title is not deemed rescinded until you manifest, by notice to the buyer or by some other overt act, an intention to rescind — an overt act works too, but silent resumption of ownership alone is not enough.
What the law says
The transfer of title shall not be held to have been rescinded by an unpaid seller until he has manifested by notice to the buyer or by some other overt act an intention to rescind.
Civil Code, Article 1534 — Unpaid Seller's Right to Rescind. Read the full provision →
When rescission by an unpaid seller is available
Article 1534 first sets the conditions for this right to exist at all: an unpaid seller having the right of lien or having stopped the goods in transitu, may rescind the transfer of title and resume the ownership in the goods, where he expressly reserved the right to do so in case the buyer should make default, or where the buyer has been in default in the payment of the price for an unreasonable time. Rescission is not automatic simply because payment is late — one of these conditions has to be met first.
Rescission takes effect only once you manifest it
Even where the right exists, the article requires an actual manifestation before rescission is deemed to have happened: the transfer of title shall not be held to have been rescinded by an unpaid seller until he has manifested by notice to the buyer or by some other overt act an intention to rescind. Simply deciding, privately, that you consider the sale rescinded is not enough — some outward manifestation of that intention is required.
Notice is not the only option, but silence carries risk
The article gives you a second route besides notice: it is not necessary that such overt act should be communicated to the buyer, but the giving or failure to give notice to the buyer of the intention to rescind shall be relevant in any issue involving the question whether the buyer had been in default for an unreasonable time before the right of rescission was asserted. So an overt act — like actually resuming physical control of the goods — can substitute for formal notice, but whether you gave notice still matters later if the default period itself is disputed.
What rescission changes between you and the buyer
Once effectively rescinded, the contract's ordinary consequences change: the seller shall not thereafter be liable to the buyer upon the contract of sale, but may recover from the buyer damages for any loss occasioned by the breach of the contract. You are freed from further obligations under the sale itself, while remaining able to pursue the buyer for damages the breach caused you.